Practice Profile

Mark was called to the Bar in 2021. He has a strong and busy practice across all of Chambers’ practice areas, including in planning and public law. Mark has a strong reputation as an advocate and, unusually for his year of call, has regularly appeared in the High Court, including as sole counsel (and will appear as sole counsel in the Court of Appeal in December). His advocacy experience, including cross-examining in the Old Bailey, means he is often instructed against more senior counsel, including KCs. He appears before a broad range of courts, tribunals and planning inquiries. He is also regularly instructed as junior counsel to other members of Chambers, including leading silks (such as Morag Ellis KC, Craig Howell Williams KC, Douglas Edwards KC, Greg Jones KC, James Periera KC, Jeremy Phillips KC and Meyric Lewis KC).

Mark is noted for his planning work, and is instructed in several forthcoming planning inquiries, including a solar farm development in the Green Belt. He is also noted for his strong experience of injunctions, including section 187B injunctions, and is regularly called upon, often urgently, to advise upon and obtain High Court injunctions. He has a broad range of clients ranging from developers and landowners to local residents. He has extensive experience of acting for, and advising, central government and local government. Recent cases include R (Dawes) v Secretary of State for Transport [2023] EWHC 2352 (Admin), Buckinghamshire Council v Twynham [2023] 7 WLUK 126, Fenland District Council v CBPRP Ltd [2022] EWHC 3132 (KB) and R (Suliman) v Bournemouth, Christchurch and Poole Council [2022] J.P.L. 1281.

During his pupillage, Mark was awarded the Reid Scholarship by Gray's Inn, a Senior Scholarship for Pupillage, which is the Inn's most prestigious scholarship and awarded to a pupil barrister of exceptional merit. He is a First Class Honours graduate of University College Dublin and the University of Cambridge. Mark was called to the Bar of Ireland in July 2023.

Mark welcomes instructions across all of Chambers' practice areas, with a particular interest in planning, public and compulsory purchase/compensation as well as licensing and environmental law.

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Mark has experience of renewable energy projects and is currently acting for a local planning authority in defending their refusal for a solar farm development in the Green Belt.

Mark successfully acted as sole counsel in the High Court for the Secretary of State for Levelling Up, Housing and Communities in defending a section 289 application for permission to appeal against the dismissal of an appeal against an enforcement notice (D&R Estates Limited v Secretary of State for Levelling Up, Housing and Communities [2022] EWHC 3595 (Admin)). He also acted as junior counsel for the Secretary of State in a challenge to the grant of development consent for the development and reopening of Manston Airport (R (Dawes) v Secretary of State for Transport [2023] EWHC 2352 (Admin)).

Mark successfully acted on behalf of a developer as junior counsel to Douglas Edwards KC in a judicial review concerning the scope and power of a local planning authority to impose conditions under the Wheatcroft and Newbury principles (R (Suliman) v Bournemouth, Christchurch and Poole Council [2022] J.P.L. 1281). The development concerned a substantial mixed use scheme including 130 residential dwellings.

Mark acted as junior counsel to Meyric Lewis KC for a local planning authority at an appeal against their refusal of planning permission for 289 residential units where the tilted balance was engaged by virtue of a five year housing land supply shortfall. Issues at the inquiry concerned proposed housing tenures and mix and whether or not the proposal achieved high quality design. 

Mark has acted as sole counsel on behalf of a local planning authority at an appeal against non-determination. He is also instructed as sole counsel for a local planning authority in a forthcoming section 78 appeal against a refusal to grant planning permission and a section 174 appeal against an enforcement notice. Mark has assisted with advising a national supermarket chain in an appeal against a refusal of planning permission.

Mark has extensive experience of dealing with contested and high-profile applications for section 187B injunctions, including regularly acting as sole counsel in the High Court. He has extensive experience of obtaining urgent interim injunctions (usually without notice) and has also obtained several permanent injunctions. He has acted in the High Court on behalf of both Claimant LPAs and a Defendant. Mark acted (as sole counsel at the interim injunction stage and as junior to Morag Ellis KC at the substantive hearing) on behalf of a large national housebuilder in successfully defending a local planning authority’s application for an injunction in circumstances where the LPA alleged that homes had been occupied prior to all highway safety works being completed as required by a condition to the planning permission for the development. 

Mark was instructed by Fenland District Council as junior counsel to Craig Howell Williams KC in an application for an interim injunction restraining a hotel from being used by a government contractor as interim accommodation for asylum seekers (Fenland District Council v CBPRP Ltd [2022] EWHC 3132 (KB)). Mark also acted as junior counsel to Craig Howell Williams KC in the High Court on behalf of Carmarthenshire County Council who also sought an injunction restraining a hotel from being used as asylum seeker accommodation. Mark also regularly appears in the High Court as sole counsel on behalf of local planning authorities seeking injunctions to restrain unauthorised gypsy/traveller developments, including in the Green Belt (e.g. Buckinghamshire Council v Twynham [2023] 7 WLUK 126).

Mark has extensive experience of enforcement matters, and in addition to his extensive experience of section 187B injunctions, he is regularly instructed in enforcement notice appeals (and has recently appeared at a hearing on behalf of a local planning authority). Mark. He has extensive experience of cases concerning an alleged material change of use. Mark has also advised a local planning authority on a high profile enforcement case prior to the issuance of an enforcement notice.

Mark has advised (as junior to Gregory Jones KC) a developer on the correct interpretation of a section 106 agreement.

He has a particular interest in, and experience of, planning work with a heritage element and several of his cases have concerned the potential impact of development on a listed heritage asset. Mark assisted with a two day judicial review challenging the decision of the Minister of State for Housing to grant planning permission for the UK Holocaust Memorial and Learning Centre next to the Houses of Parliament (London Historic Parks And Gardens Trust v Minister of State for Housing & Anor [2022] EWHC 829 (Admin)). Mark has advised the owner of a country estate on a redevelopment proposal for part of the estate and advised the owner of a Grade I country home on objecting to a nearby planning application.

Mark assisted at a section 247 stopping up and diversion order inquiry which raised several issues, including parking, highway safety and impact upon heritage assets. 

Mark also assisted at a planning inquiry dealing with inappropriate development (a gypsy/traveller site) in the Green Belt and within an Area of Outstanding Natural Beauty. The inquiry was concerned with an appeal against a refusal of planning permission and also with an appeal against an enforcement notice. He is instructed by a local planning authority in a forthcoming gypsy/traveller inquiry. 

Mark has assisted at a planning inquiry considering the merits of a large residential housing development in a semi-rural location. The inquiry considered the impact upon character and appearance, the impact upon a Grade II* listed building, highway safety and biodviersity. 

Mark has extensive experience of Certificates of Lawful Existing Use or Development and is acting on behalf of the Appellant in a forthcoming inquiry. He regularly advises both applicants for CLEUDs and LPAs who are determining applications.

Mark has advised on a number of issues, including the implementation of planning permissions, pre-commencement conditions, conditions precedent, enforcement notices, appeals against enforcement notices, immunity from enforcement action, certificates of lawfulness, changes of use, prior approval, permitted development rights, the precautionary principle and the scope of amendments under section 73 of the Town and Country Planning Act 1990. He also assisted with preparations for defending a judicial review challenging a Special Development Order. 

Mark has extensive experience of permitted development rights and has advised, as junior counsel, the Home Secretary on the exercise of permitted development rights in the context of asylum seeker accommodation. He has also acted as sole counsel in an application for judicial review concerning telecommunications infrastructure and permitted development rights.

Mark has gained extensive experience of environmental law and is a frequent contributor to FTB’s Environmental Law Blog as well as being a member of the Editorial Board. Mark has experience of successfully prosecuting, as sole counsel, a criminal offence under the Environmental Protection Act 1990.

Mark acted as junior counsel for the Secretary of State in a challenge to the grant of development consent for the reopening of Manston Airport (R Dawes) v Secretary of State for Transport [2023] EWHC 2352 (Admin)) which concerned, inter alia, climate change.

Mark assisted with defending a judicial review brought by Plan B Earth and four claimants challenging the lawfulness of the government’s action on climate change as breaching sections 13 and 58 of the Climate Change Act 2008 and section 6 of the Human Rights Act 1998 by way of the ECHR (Articles 2, 8, and 14). The Court was also required to address the status of the Paris Agreement as an unincorporated international treaty. 

Mark assisted with defending a complex and high profile three day judicial review before the Divisional Court in which Friends of the Earth challenged the decision of UK Export Finance, along with the prior approval of the Secretary of State for International Trade and the Chancellor of the Exchequer, to provide up to US$1.15bn in export finance and support for a US$20bn liquified natural gas field in Northern Mozambique. The judicial review was primarily concerned with the Paris Agreement. 

Mark assisted with preparations for defending several judicial review challenges brought by NGOs to the government’s Net Zero Strategy. 

Mark has also gained experience of dealing with the SEA and EIA Directives and Regulations and the Aarhus Convention. He also has experience of the Environmental Information Regulations 2004.

Mark is a member of the Attorney General’s ‘Junior’ Junior Scheme and is regularly instructed to advise the government on a broad range of public law matters. He has also acted on behalf of the Metropolitan Police as sole counsel in an application for judicial review before the High Court.

Mark has extensive experience across a wide range of public law areas and has assisted with judicial reviews raising both substantive and procedural public law issues, including the public sector equality duty and the doctrine of legitimate expectation.  

Mark acted as junior counsel to Douglas Edwards KC in a judicial review concerning whether, on the facts of the case, a legitimate expectation had arisen (R (Suliman) v Bournemouth, Christchurch and Poole Council [2022] EWHC 1196 (Admin)). Mark acted as junior counsel for the Secretary of State in a challenge to the grant of development consent for Manston Airport (R Dawes) v Secretary of State for Transport [2023] EWHC 2352 (Admin)) in which the Court was concerned with the question of procedural unfairness.

Mark is currently instructed as junior counsel to James Pereira KC on behalf of a Claimant in a compensation claim concerning a high value mixed-use development scheme. He has appeared as sole counsel before the Upper Tribunal (Lands Chamber).

Mark has experience of Certificates of Appropriate Alternative Development and is currently acting as junior counsel to James Pereira KC in an ongoing CAAD appeal before the Lands Chamber.

Mark has assisted with a wide range of compulsory purchase and compensation matters. During the course of his pupillage, he has gained extensive experience of compulsory purchase and compensation cases. He has gained experience of a number of complex issues, including transfer of trade, compensation for disturbance, the compulsory acquisition of open space, potential exchange land sites and the applicability of Bishopgate.  

Mark assisted with a mediation in respect of a multi-million claim for compensation. 

Mark has extensive experience in licensing matters. He has appeared before several Licensing Sub-Committees and has dealt with many sensitive cases, including an application for a summary review following a high-profile murder. He has been instructed to act in both review hearings and summary review hearings of licensed premises. He also has extensive experience of dealing with Closure Orders in respect of licensed premises. Mark has acted for applicants, responsible authorities and also for interested parties, including local residents.

Mark also has extensive experience of Private Hire Vehicles. He has acted on behalf of Transport for London in appeals against refusals of PHV licences (in the Old Bailey). He has also advised an international ride-hailing service, as junior to Jeremy Phillips, on their regulatory obligations under the Private Hire Vehicles (London Act) 1998.

 

Mark successfully obtained a possession order against trespassers on behalf of National Highways Limited. The case concerned a protest against the upgrading of a major trunk road in Somerset and was the subject of extensive media interest. 

Mark acted as sole counsel on behalf of the Applicant in a two day Definitive Map Modification Order inquiry involving highway issues. Mark acted as junior counsel to Douglas Edwards KC in an inquiry objecting to an application for consent under Article 12 of the Greater London Parks and Open Spaces Order 1967 to create a temporary event site on Clapham Common to facilitate a music festival.

Mark has assisted with an application for an order pursuant to section 56 of the Highways Act 1980.

Mark has advised a Welsh local authority on objections made to its application pursuant to section 38 of the Commons Act 2006 to construct a shared use path as part of the Council’s Active Travel project.

Mark acted as junior counsel for the Secretary of State in a widely publicised challenge to the grant of development consent for the development and reopening of Manston Airport (R Dawes) v Secretary of State for Transport [2023] EWHC 2352 (Admin)) as a dedicated air freight facility. Amongst the issues for the Court was the correct interpretation of the Infrastructure Planning (Examination Procedure) Rules 2010. The Claimant also challenged the Secretary of State’s assessment of need, and in particular his departure from the conclusions of the Examining Authority.  

Mark has advised the Department of Transport on the examination of an application for a Development Consent Order made by National Highways for the A66 Northern Trans-Pennine Project.

Mark has a particular interest in, and experience of, injunction work. He is regularly instructed to act on behalf of local planning authorities seeking a section 187B injunction. He has also acted on behalf of a defendant national housebuilder (as junior to Morag Ellis KC) in successfully resisting an application for an injunction. He regularly appears as sole counsel in the High Court, and has experience of seeking, and resisting, urgent interim injunctions. Mark has extensive experience of dealing with urgent matters at short notice (including appearing before the out of hours judge in the High Court as junior to Craig Howell Williams KC). Mark also has experience of advising upon gang injunctions under the Policing and Crime Act 2009.

Mark assisted with a two day judicial review concerning social housing relief under the Community Infrastructure Levy Regulations 2010 and the consequences of a failure to submit a commencement notice. 

Mark also assisted with a Court of Appeal hearing concerning the self-build housing exemption under the Regulations. He has also assisted with advising in writing on CIL Liability.

Mark advises police authorities on numerous civil orders and regularly appears before the Magistrates' Court and the Crown Court as sole counsel (including successfully acting against a leading criminal KC). He has experience of successfully obtaining Closure Orders, Stalking Prevention Orders and orders under the Sexual Offences Act 2003 including Sexual Harm Prevention Orders and Sexual Risk Orders for the Metropolitan Police. He has particular experience of dealing with high profile and sensitive situations on behalf of the police. He has also acted on behalf of the Metropolitan Police as sole counsel in an application for judicial review before the High Court. He regularly acts as Legal Advisor to Licensing Sub-Committees which offers him a unique perspective on the determination of licensing matters. Mark also has experience of the Proceeds of Crime Act 2002.

Mark successfully obtained a possession order against trespassers on behalf of National Highways Limited. The case concerned a protest against the upgrading of a major trunk road. 

Mark has experience of statutory nuisance and has been instructed in an appeal against an abatement notice.  

Mark has acted (as junior counsel to Jeremy Phillips KC) in a misrepresentation claim.

Mark has an interest in regulatory and disciplinary work. Mark has been instructed as Independent Counsel to advise on legal professional privilege in relation to material seized as part of an investigation concerning a leading political figure who was accused of sexual misconduct.  

Mark is part of the team teaching the Public Inquiry Workshop at Oxford University.

  • BCL Law with History 2019, University College Dublin, First Class Honours 
  • Bar Professional Training Course, September 2019 – August 2020, BPP University Law School, Outstanding
  • LLM (Master of Law), University of Cambridge, October 2020 – June 2021, First Class Honours. Papers included International Environmental Law and Information Law
  • Awarded the Reid Scholarship by Gray's Inn, a Senior Scholarship for Pupillage which is the Inn's most prestigious scholarship and awarded to a pupil barrister of exceptional merit
  • Elected by the Governing Body of Queen’s College, Cambridge to a Foundation Scholarship
  • Awarded a full scholarship plus maintenance (the Snowdon Cambridge Scholarship 2020) by the Cambridge Trust to undertake an LLM (Master of Law) at the University of Cambridge
  • The Baroness Hale of Richmond BPTC Scholarship 2019, awarded by The Honourable Society of Gray's Inn, is the Inn’s newest and most prestigious scholarship. It is awarded to candidates of exceptional merit
  • The BPTC Advocacy Scholarship 2019 is awarded by BPP University Law School to those who demonstrate an outstanding aptitude for advocacy
  • The Career Commitment Scholarship 2019 is awarded by BPP University Law School to those who are considered to be the most promising future legal professionals
  • The Jomati Foundation Bursary 2019, awarded by the Jomati Foundation, assists students of high academic ability with the costs of qualifying as a barrister
  • The Hebe Plunkett Award 2019, awarded by The Honourable Society of Gray's Inn
  • Irish Law Student of the Year 2019 awarded at the Irish National Law Awards in recognition of academic, professional and personal achievements
  • The Gold Medal for Mooting 2017 which is awarded by the University College Dublin Law Society to the student most successful in mooting in the previous academic year
  • Certificate in Work Related Learning (Commercial Law in the City of London) 2017 awarded by the University College Dublin Career Development Centre

Mooting

  • Winner of the 2021 Cambridge University Human Rights Law Moot
  • Winner of the 2018 Irish National Moot Court Competition which was judged by a Supreme Court and High Court judge
  • Winner of the 2017 Silken Thomas National Moot Court and the 2016 Vivian Lavan Moot Court Competition, which were judged by a District and Circuit Court Judge respectively 
  • Best Advocate of the 2017 Cecil Lavery Moot Court 
  • Runner-up of the 2016 University College Dublin Pro-Am Moot Court 
  • Semi-finalist of the 2017 National Moot Court Competition, the 2016 University College Cork Moot Court Open and the 2017 Cecil Lavery Moot Court 
  • Attended a Stetson Law School advocacy training course on the art of mastering cross examination in July 2017 
  • Invited to judge several mooting competitions at the University of New South Wales

Debating and public speaking

  • Addressed the launch of the University College Dublin Sutherland Opportunity in December 2019, a new scholarship opportunity providing financial support to enable students from under-represented groups to pursue a career in law
  • Winner of the 2016 National De Valera Cup for Debating 
  • Finalist of the 2015 University College Dublin Intervarsity Novice Debating Competition 
  • Semi-finalist of the 2016 Irish Times National Debating Competition 
  • Semi-finalist of the 2015 James Joyce Maidens' Debating Competition 
  • Represented the University College Dublin Law Society as a judge at the European Universities Debating Championships in August 2016 
  • Participated in various international debating competitions 
  • Spoke in several house debates at university 
  • Captain of the St Patrick’s Classical School debating team 
  • Chosen to act as valedictorian at school graduation ceremony due to public speaking ability and academic achievements 

Negotiation

  • Winner of the European Law Students’ Association Maynooth International Negotiation Competition in March 2019. As part of team of two, defeated a team from Georgetown University, Washington D.C. in the final 
  • Finalist of the University College Dublin Student Legal Service McCann FitzGerald Commercial Negotiation Competition in November 2017, having previously been a semi-finalist in November 2016 
  • Constitutional & Administrative Law Bar Association (ALBA) 
  • UK Environmental Law Association (UKELA)
  • London Irish Lawyers Association
  • The Planning and Environmental Bar Association (PEBA)
  • The Ireland Funds (Great Britain) 
  • Occasional Lecturer at Maynooth University, September 2021
  • Executive Assistant to the Director of Summer at UCD, University College Dublin Estates Services (summer 2019)
  • Mark spent time working as a vacation scheme student at leading law firms including Freshfields Bruckhaus Deringer, Mason Hayes & Curran LLP and Herbert Smith Freehills where he worked on large-scale, long-term infrastructure and energy projects

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21
May' 24
Court of Appeal Refuses an Appeal Against High Court’s Decision to Dismiss a Judicial Review of the Grant of Development Consent for Manston Airport - R (Dawes) v Secretary of State for Transport [202

The Court of Appeal (Lewis, Jackson and Warby LJs) has today dismissed an appeal against the decision of Mr Justice Dove to dismiss a judicial review of the decision of the Secretary of State for Transport to grant development consent for the development and reopening of Manston Airport in Kent as a dedicated air freight facility.

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30
Apr' 24
Successful Application For a Section 187B Injunction - Chelmsford CC and Braintree DC v Mixture [2024] EWHC 1006 (KB)

The High Court (Saini J) has today handed down judgment in Chelmsford CC and Braintree DC v Mixture [2024] EWHC 1006 (KB) in which Mark O'Brien O'Reilly acted for the successful Claimants.

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29
Jan' 24
Planning Injunctions Against Persons Unknown After Wolverhampton City Council v London Gypsies and Travellers – the High Court Decision in Buckinghamshire Council v Barrett [2024] EWHC 140 (KB)

In what is likely the first decided case of this nature since the Supreme Court handed down its judgment in Wolverhampton City Council v London Gypsies and Travellers [2023] UKSC 47, the High Court has considered an application for a planning injunction against persons unknown, as well as against a named defendant. 

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07
Mar' 23
CJEU Case Law – Recent Important Environmental Law Cases Post-Brexit

English lawyers would be well advised to cast their eyes south of Dover and across the water to the Court of Justice of the European Union (“CJEU”). Although the United Kingdom has left the European Union, the caselaw of the CJEU still has an important role to play in environmental litigation within domestic courts. 

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21
Dec' 22
The COP27 Summit

The COP27 Summit in Sharm el-Sheikh, which took place in the midst of conflict in Ukraine and an energy crisis, concluded in late November 2022 with a number of notable developments, despite the fact that the State parties failed to commit to phasing out fossil fuels. 

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09
Nov' 22
Harris v The Environment Agency [2022] EWHC 2606 (Admin) - Remedies

In my blogpost dated 23 September 2022, I analysed the judgment in Harris v The Environment Agency [2022] EWHC 2264 (Admin) of 6 September 2022, which illustrated the application of the EU Habitats Directive, and of European law more widely, post-Brexit.

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23
Sep' 22
Harris v The Environment Agency [2022] EWHC 2264 (Admin)

Johnson J has handed down judgment in Harris v The Environment Agency [2022] EWHC 2264 (Admin). The judgment illustrates the application of the EU Habitats Directive, and of European law more widely, post-Brexit. 

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