Cross-Border Energy Cooperation After Brexit

1. Introduction

Cross-border energy cooperation after Brexit refers to the legal and regulatory relationship between the United Kingdom and the European Union in electricity, gas, renewable energy, nuclear energy and energy infrastructure after the UK left the EU.

Brexit did not end energy cooperation. However, it changed the legal framework. From 1 January 2021, Great Britain left the EU Internal Energy Market and could no longer use the EU's normal market-coupling mechanisms for electricity trading. Northern Ireland remained connected to the Single Electricity Market with Ireland under the Withdrawal Agreement arrangements. (Energy)

Therefore, post-Brexit cooperation is based mainly on the EU-UK Trade and Cooperation Agreement (TCA), regulatory cooperation, interconnector arrangements and separate agreements concerning particular energy sectors.

2. EU-UK Trade and Cooperation Agreement

The TCA created a framework for continuing energy cooperation between the UK and EU. Its Energy Title covers areas such as:

electricity and gas trade;

security of energy supply;

renewable energy;

energy efficiency;

electricity interconnectors;

offshore renewable energy;

regulatory cooperation; and

development of new electricity-trading arrangements.

The TCA requires the UK and EU to work towards efficient electricity trading over interconnectors. (GOV.UK)

This is important because electricity cannot be traded efficiently simply by having physical cables. The legal and market systems on both sides must also cooperate.

3. Changes in Electricity Trading

Before Brexit, Great Britain participated in the EU Internal Electricity Market and benefited from market coupling. Market coupling allows electricity prices and cross-border transmission capacity to be coordinated through common European systems.

After Brexit, Great Britain stopped participating in these EU market-coupling mechanisms. Electricity could still flow through interconnectors, but the trading arrangements became more complicated.

The European Commission explains that electricity trading between Great Britain and the EU now operates through arrangements different from the EU's internal market system. The TCA provides for transmission system operators to develop new arrangements based on multi-regional loose volume coupling. (Energy)

The UK government similarly recognises that post-Brexit interconnector trading involves greater complexity because electricity and interconnector capacity are generally traded separately. (GOV.UK)

4. Role of Regulators and Transmission Operators

Cross-border energy cooperation requires cooperation between regulators and transmission system operators.

In the UK, Ofgem works with European regulatory authorities, while NESO works with transmission system operators in connected countries.

The TCA created institutional mechanisms, including the Specialised Committee on Energy, to supervise and facilitate cooperation. The UK government states that the committee oversees implementation of the TCA's energy provisions and work on future electricity-trading arrangements. (GOV.UK)

This creates a form of multi-level energy governance involving governments, regulators, transmission operators and market participants.

5. Northern Ireland and the Single Electricity Market

Northern Ireland is legally significant because its position differs from Great Britain.

The Withdrawal Agreement preserved the operation of the Single Electricity Market (SEM) on the island of Ireland. This allows Northern Ireland and Ireland to continue operating a shared electricity market despite Brexit. (GOV.UK)

Thus, post-Brexit energy law does not create one uniform UK-EU electricity relationship. There is an important distinction between:

Great Britain–EU: separate electricity markets with new trading arrangements.

Northern Ireland–Ireland: continued operation of the Single Electricity Market under the Withdrawal Agreement framework.

6. Renewable Energy and Offshore Cooperation

Brexit has not removed cooperation concerning renewable energy. The TCA includes cooperation concerning offshore renewable energy, particularly in the North Sea and Irish Sea.

This is increasingly important because offshore wind projects can involve several countries and may require hybrid infrastructure connecting renewable generation with multiple electricity markets.

The UK and neighbouring European countries have also continued regional cooperation concerning North Sea energy infrastructure. (Energy)

7. Nuclear Energy Cooperation

The UK also left Euratom, meaning that nuclear cooperation required a separate legal framework.

The EU and UK concluded a separate agreement concerning cooperation on the safe and peaceful use of nuclear energy. This covers matters connected with nuclear safety, safeguards, research and nuclear-related cooperation. (Energy)

This demonstrates that Brexit affected not only electricity trading but also the institutional structure for nuclear-energy cooperation.

8. Relevant Case Laws

VEMW and Others v Directeur van de Dienst uitvoering en toezicht energie, Case C-17/03

This EU case concerned preferential access to electricity transmission capacity under long-term electricity contracts.

The Court of Justice examined whether national arrangements could give particular electricity traders preferential access to cross-border transmission capacity.

Relevance: It demonstrates the importance of non-discriminatory access to cross-border electricity networks and the relationship between national electricity arrangements and EU internal-market rules.

Ålands Vindkraft AB v Energimyndigheten, Case C-573/12

The case concerned Sweden's renewable-energy certificate scheme and electricity generated in another Member State.

The Court examined the interaction between national renewable-energy support and EU free-movement rules.

Relevance: It shows that national renewable-energy policies can have significant effects on cross-border electricity trade.

Essent Belgium NV v Vlaamse Reguleringsinstantie, Joined Cases C-204/12 to C-208/12

The litigation concerned national measures affecting electricity suppliers and cross-border electricity activities.

Relevance: The case illustrates the importance of EU rules governing electricity markets and the limits on national measures that interfere with the internal electricity market.

These cases arose before or independently of Brexit, but they remain useful for understanding the legal principles governing cross-border electricity markets that the post-Brexit UK-EU relationship must now accommodate through different institutional arrangements.

9. Developments in 2025–2026

The post-Brexit relationship continues to evolve. In December 2025, exploratory discussions concerning possible UK participation in the EU Internal Electricity Market were concluded, and in 2026 the EU moved toward formal negotiations on UK participation. (GOV.UK)

The UK government's March 2026 policy also identifies closer electricity-market cooperation as an important future issue, particularly for improving interconnector efficiency and supporting renewable-energy development. (GOV.UK)

This means the legal relationship is not static; it continues to develop through negotiations and institutional cooperation.

10. Conclusion

Cross-border energy cooperation after Brexit operates through a complex combination of the TCA, the Withdrawal Agreement, domestic UK law, EU law, regulatory cooperation and international energy arrangements.

The main legal challenge is maintaining efficient electricity flows while the UK and EU operate partly separate regulatory and market systems. Interconnectors, renewable energy, offshore infrastructure, nuclear cooperation and security of supply all require continuing coordination.

For energy-law research, Brexit therefore provides an important example of how withdrawal from a supranational legal system can change cross-border energy governance without eliminating the underlying need for regional energy cooperation.