1. Introduction

The future of UK–EU electricity cooperation is likely to move beyond the limited post-Brexit model of separate electricity markets connected by interconnectors. Since the end of the Brexit transition period, Great Britain has no longer participated in the EU internal electricity market or EU market-coupling mechanisms. Electricity continues to flow between Great Britain and EU countries through interconnectors, but trading arrangements are more complicated than before Brexit. (Energy)

The principal legal framework is currently Title VIII (Energy) of the EU–UK Trade and Cooperation Agreement (TCA). The TCA provides for cooperation concerning electricity trading, interconnectors, security of supply, renewable energy and regulatory cooperation. In June 2025, the UK and EU extended the Energy Title to 31 March 2027. (GOV.UK)

A significant development occurred in 2025–2026. Following the May 2025 UK–EU Summit, the parties explored UK participation in the EU internal electricity market (IEM). Exploratory discussions concluded in December 2025, and in March 2026 the EU Council authorised negotiations on an agreement concerning UK participation in the EU internal electricity market. (EUR-Lex)

Thus, future UK–EU electricity cooperation may develop around five interconnected pillars:

closer electricity-market integration;

improved cross-border electricity trading;

regulatory alignment;

North Sea offshore-grid cooperation; and

coordinated energy-security and resilience arrangements.

2. Post-Brexit Legal Background

Before Brexit, Great Britain participated in the EU's internal energy market. Electricity trading was supported by EU market-coupling mechanisms, common rules on cross-border capacity allocation, congestion management and regulatory cooperation.

After the transition period ended on 31 December 2020, Great Britain left the EU internal energy market. The EU explains that electricity trading between Great Britain and EU Member States is consequently no longer managed through the EU's ordinary single-market coupling mechanisms. (Energy)

The TCA attempted to create a new framework for cooperation.

Article 299 TCA

Article 299 establishes broad objectives of energy cooperation, including:

facilitating trade and investment;

supporting security of supply;

promoting environmental sustainability; and

contributing to climate objectives.

Articles 311–312 TCA

These provisions are particularly important for electricity.

They establish principles concerning:

efficient use of electricity interconnectors;

electricity trading;

capacity allocation;

congestion management; and

development of new trading arrangements.

The TCA contemplated a Multi-Region Loose Volume Coupling (MRLVC) mechanism for day-ahead electricity trading. However, implementation has proved technically and institutionally difficult. (EUR-Lex)

3. Future Participation in the EU Internal Electricity Market

The most important potential development is a future UK–EU Electricity Agreement.

The UK and EU's December 2025 exploratory discussions concluded that they should work towards UK participation in the EU internal electricity market through such an agreement. (GOV.UK)

The proposed framework is significant because it could move cooperation from a relatively limited intergovernmental model towards structured participation in EU electricity-market mechanisms.

The exploratory outcome envisages:

UK participation in relevant EU electricity trading platforms;

regulatory cooperation;

access to relevant EU systems and databases;

participation by the relevant UK regulatory authority in ACER without voting rights;

financial contribution by the UK;

dynamic alignment with relevant EU electricity-market rules;

joint governance; and

dispute settlement involving an independent arbitration mechanism while preserving the CJEU's ultimate authority on questions of EU law. (GOV.UK)

This is potentially a major institutional innovation: the UK would remain outside the EU politically while becoming more closely integrated into a specific EU regulatory market.

4. Electricity Trading Cooperation

One of the central problems after Brexit is the efficiency of electricity trading.

Under the present arrangements, electricity and interconnector capacity are traded through separate processes. The UK Government has acknowledged that this can create complexity and potentially inefficient electricity flows. (GOV.UK)

Future cooperation could therefore involve:

A. Improved market coupling

The UK could obtain greater access to EU trading platforms, potentially reducing the separation between:

electricity price formation + interconnector capacity allocation.

This could improve the economic utilisation of existing interconnectors.

B. Intraday cooperation

Greater integration of intraday markets would be particularly valuable because renewable generation can change rapidly.

Wind and solar generation create forecasting uncertainty. More integrated intraday markets could allow electricity to move across borders closer to real time.

C. Balancing cooperation

Future arrangements could also facilitate cooperation between transmission-system operators in balancing electricity systems.

This becomes increasingly important as the share of variable renewable generation rises.

5. Multi-Region Loose Volume Coupling

The TCA envisaged MRLVC as a method for improving day-ahead electricity trading.

The concept attempts to approximate the efficiency of EU market coupling while operating between two legally distinct markets.

However, the UK and EU have experienced difficulties in developing the mechanism. The parties moved towards a concept-validation phase and established roadmaps for further work. (GOV.UK)

The future UK–EU Electricity Agreement could potentially make MRLVC less important if the UK obtains direct participation in relevant EU trading arrangements.

Consequently, there are two possible regulatory trajectories:

Model 1:
TCA + MRLVC + separate markets.

Model 2:
Closer UK participation in the EU internal electricity market + deeper market coupling.

The second model is currently the subject of formal negotiations, but its final legal form remains to be determined. The EU Council authorised negotiations in March 2026. (EUR-Lex)

6. Role of ACER and Ofgem

Future cooperation will require institutional coordination.

The relevant EU institution is the Agency for the Cooperation of Energy Regulators (ACER), while Ofgem is the principal electricity and gas regulator for Great Britain.

The exploratory UK–EU framework proposes participation of the relevant UK regulatory authority in ACER without voting rights and an extension of ACER's regulatory oversight in areas covered by the Electricity Agreement. (GOV.UK)

This creates an important constitutional question:

How can a non-EU state participate in an EU regulatory system while remaining outside the EU institutional structure?

The likely answer is a hybrid governance model involving:

UK regulatory participation;

information exchange;

consultation during EU rule development;

dynamic regulatory alignment;

financial contribution; and

dispute settlement.

The UK Government has also identified Ofgem's role in facilitating cooperation with ACER and neighbouring national regulatory authorities. (GOV.UK)

7. Dynamic Alignment of Electricity Regulation

A future agreement may require the UK to maintain rules compatible with relevant EU electricity legislation.

This could concern:

electricity trading;

cross-border capacity;

congestion management;

balancing;

market transparency;

network codes;

system operation;

consumer protection;

data exchange; and

renewable-energy integration.

The legal difficulty is that dynamic alignment can create a form of regulatory dependence without EU membership.

The exploratory agreement therefore envisages mechanisms allowing the UK to contribute at an early stage to the shaping of relevant EU legislation, although without participation in the Council itself. (GOV.UK)

This represents a compromise between:

EU regulatory autonomy
and
UK participation in the electricity market.

8. North Sea Offshore Electricity Cooperation

The North Sea is likely to become one of the most important areas of UK–EU energy cooperation.

The UK and European states are developing offshore wind at enormous scale. Future offshore infrastructure may involve:

offshore wind farms;

cross-border interconnectors;

hybrid offshore projects;

electricity hubs;

energy islands;

hydrogen production;

offshore grids; and

multi-country electricity transmission.

The UK participates in cooperation with the North Seas Energy Cooperation (NSEC) through a 2022 Memorandum of Understanding. NSEC provides a framework for offshore renewable cooperation, although it is not itself a binding EU internal-market regime. (Energy)

At the January 2026 North Sea Summit, the UK and European partners reaffirmed cooperation concerning offshore renewable energy, cross-border infrastructure and security of energy infrastructure. (GOV.UK)

Future legal arrangements may therefore need rules concerning:

allocation of offshore grid costs;

ownership of hybrid assets;

permitting;

cross-border environmental assessment;

liability;

transmission charging;

congestion;

electricity dispatch;

offshore wind-to-grid connections;

cybersecurity; and

emergency response.

9. Security of Electricity Supply

Energy security is another central pillar.

The UK and EU have already developed cooperation on security of supply, including dialogue concerning winter preparedness and a Security of Supply Working Group. (GOV.UK)

Future cooperation could develop into a more formal security framework covering:

Emergency electricity shortages

The parties could establish mechanisms for:

information exchange;

emergency notifications;

coordinated responses;

mutual assistance; and

prioritisation of critical infrastructure.

Infrastructure disruption

The framework could address:

physical attacks;

cyberattacks;

subsea cable damage;

offshore infrastructure disruption; and

hybrid threats.

This is particularly significant because modern electricity systems are increasingly dependent on interconnected digital infrastructure.

10. Interconnectors as Legal Infrastructure

Interconnectors are not merely physical cables. They are regulated legal-economic systems involving:

transmission rights;

capacity allocation;

congestion management;

tariffs;

market coupling;

balancing;

system security; and

regulatory supervision.

The UK Government has stated that interconnectors can improve affordability, energy security, decarbonisation and system flexibility. (GOV.UK)

Future UK–EU arrangements will therefore need to establish predictable rules for both existing and new interconnectors.

Important existing connections include links involving France, Belgium, the Netherlands and Ireland. The EU notes the continuing deep interconnection between UK and EU electricity systems. (Energy)

11. Legal Case Law

There is relatively little reported case law directly concerning a future UK–EU electricity agreement because the proposed agreement is still under negotiation. However, existing UK and EU cases provide important legal principles for its construction.

Case 1: SSE Generation Ltd v Competition and Markets Authority [2022] EWCA Civ 1472

This is particularly relevant to future UK–EU electricity cooperation.

The case concerned electricity transmission charges and the interpretation of congestion management.

The Court of Appeal considered the relationship between:

electricity transmission charges;

congestion;

interconnectors;

EU electricity legislation; and

post-Brexit retained EU law.

The court recognised the significance of maintaining coherent regulatory principles across interconnected electricity systems. It observed that divergent charging rules could create distortions in pricing signals and affect the free flow of energy and investment decisions. (BAILII)

Importance

The case demonstrates that electricity-law divergence is not merely a technical legal issue.

Different regulatory definitions can produce:

different charges → different market signals → different electricity flows → different investment incentives.

That principle is highly relevant to the future UK–EU relationship.

Case 2: BNetzA and Germany v ACER, Joined Cases T-600/23 and T-612/23, judgment of 1 October 2025

This General Court case concerned:

the EU internal electricity market;

cross-zonal capacity allocation;

congestion management;

ACER;

transmission-system operators; and

calculation of cross-border electricity capacity.

The General Court partially annulled an ACER decision concerning methodologies for calculating day-ahead and intraday cross-zonal capacity. (InfoCuria)

Importance for UK–EU cooperation

The case illustrates the highly technical and legally structured character of EU cross-border electricity regulation.

A future UK participation agreement would therefore need to deal carefully with:

ACER's powers;

TSO methodologies;

cross-zonal capacity;

congestion management;

regulatory review; and

judicial or arbitral oversight.

Case 3: TenneT TSO GmbH and TenneT TSO BV v ACER, Case T-482/21

The General Court considered EU electricity-market rules concerning the methodology for sharing the costs of redispatching and countertrading.

The case demonstrates the legal significance of cross-border congestion management and allocation of costs among transmission-system operators. (InfoCuria)

Importance

Future UK–EU electricity cooperation will have to answer a similar question:

When cross-border electricity flows create congestion or require corrective action, who bears the resulting costs?

This becomes even more complicated for hybrid offshore projects involving multiple jurisdictions.

Case 4: CRE v ACER, Case T-446/21

The General Court also examined ACER's approach to redispatching, countertrading and legitimate loop flows in the EU electricity market. (InfoCuria)

The case illustrates the importance of transparent and legally justified methodologies when EU regulatory agencies make technically complex electricity-market decisions.

For a future UK–EU agreement, this supports the need for:

transparent methodologies;

reasoned regulatory decisions;

effective review mechanisms; and

predictable allocation of cross-border costs.

Case 5: Swissgrid AG v European Commission, Case C-121/23 P

This case concerned Switzerland, another non-EU state deeply interconnected with the European electricity system.

The dispute concerned participation by a Swiss transmission-system operator in European balancing platforms. The Court examined the legal framework governing participation in EU electricity-balancing arrangements. (InfoCuria)

Importance for the UK

Although Switzerland and the UK have different legal relationships with the EU, the case demonstrates the fundamental legal problem facing non-EU participation:

Physical interconnection does not automatically create a legal right to participate in EU electricity-market mechanisms.

Participation depends upon the applicable EU legal framework and institutional arrangements.

This is directly relevant to the proposed UK Electricity Agreement.

Case 6: AEM SpA and AEM Torino SpA, Joined Cases C-128/03 and C-129/03

The CJEU examined electricity transmission-system access and the principle of non-discrimination under EU internal electricity-market law.

The case demonstrates the longstanding importance of:

non-discriminatory network access;

electricity-market liberalisation; and

common regulatory principles.

These principles remain relevant to cross-border electricity cooperation.

12. Northern Ireland and the Single Electricity Market

Northern Ireland presents a distinctive legal situation.

Unlike Great Britain, Northern Ireland remains subject to certain EU electricity-market rules under the Windsor Framework. The EU's 2026 decision notes that relevant EU wholesale electricity-market rules continue to apply in Northern Ireland under the framework. (EUR-Lex)

This creates an unusual legal structure:

Great Britain → outside EU internal electricity market

Northern Ireland → certain EU electricity rules continue to apply

This distinction is highly relevant to future UK–EU electricity governance.

It creates a need for coordination between:

UK legislation;

EU electricity law;

Northern Ireland arrangements;

the Single Electricity Market on the island of Ireland; and

the wider UK–EU electricity relationship.

13. Future Governance Model

A future UK–EU electricity framework could develop into a hybrid transnational regulatory regime.

A possible structure would be:

Level 1 — Political governance

UK–EU political institutions establish broad objectives concerning:

energy security;

decarbonisation;

electricity affordability;

infrastructure;

offshore renewables.

Level 2 — Joint electricity governance

A UK–EU Electricity Committee could supervise implementation.

Level 3 — Regulatory cooperation

Ofgem, ACER and European national regulators could cooperate on:

market rules;

network codes;

congestion;

balancing;

data;

system security.

Level 4 — TSO cooperation

National and regional transmission operators could coordinate:

capacity;

system operation;

balancing;

offshore networks;

emergency responses.

Level 5 — Judicial and dispute settlement

An independent dispute mechanism could operate, while questions of EU law would remain subject to the interpretative authority of the CJEU as contemplated by the exploratory outcome. (GOV.UK)

14. Major Legal Challenges

1. Regulatory sovereignty

The UK would need to balance participation in EU electricity structures with its post-Brexit regulatory autonomy.

2. Dynamic alignment

If EU electricity legislation changes, the future agreement must determine whether and how UK rules change.

3. Institutional participation

The UK may participate in ACER-related processes without possessing EU Member State voting rights.

4. Dispute settlement

The parties must determine how disputes involving EU electricity legislation are resolved.

5. Financial contributions

The exploratory framework contemplates an appropriate UK financial contribution connected with participation in the EU electricity market. (GOV.UK)

6. Data sharing

Efficient electricity markets require substantial exchange of operational and market data.

7. Offshore infrastructure

Hybrid offshore projects raise complex questions about ownership, planning, environmental law, transmission charging and liability.

15. Future Legal Significance

The future UK–EU electricity relationship is likely to represent a broader transformation in energy law.

The traditional model was:

national electricity market → national regulator → national infrastructure

The future model is increasingly:

interconnected electricity market → cross-border regulator cooperation → shared infrastructure → coordinated system security.

This means that sovereignty in electricity law will increasingly operate through cooperative regulatory institutions, rather than purely through territorial control.

The proposed UK participation agreement is particularly important because it could create a model in which a non-EU country participates substantially in an EU market without becoming an EU Member State.

16. Conclusion

Future UK–EU electricity cooperation is moving towards a more integrated legal and regulatory framework. The current TCA provides the foundation, but its electricity-trading mechanisms have not completely reproduced the efficiency of the former EU market-coupling arrangements. The UK and EU have therefore moved towards negotiations on a possible agreement allowing UK participation in the EU internal electricity market. (EUR-Lex)

The likely future framework will involve electricity-market participation, interconnector efficiency, regulatory cooperation, ACER–Ofgem coordination, dynamic alignment, security-of-supply mechanisms and North Sea offshore-grid cooperation.

The developing jurisprudence is also significant. SSE Generation v CMA demonstrates the consequences of regulatory divergence in interconnected electricity systems, while BNetzA v ACER, TenneT v ACER, CRE v ACER and Swissgrid v Commission demonstrate the increasingly sophisticated legal structure governing cross-border electricity markets and participation by non-EU systems. (BAILII)

Ultimately, the future UK–EU electricity regime is likely to be neither complete separation nor restoration of pre-Brexit membership. It is more likely to involve a specialised, treaty-based form of regulatory and market integration, designed around the practical reality that electricity networks transcend political borders.

Key legal authorities: EU–UK Trade and Cooperation Agreement, Articles 299–312; Windsor Framework; UK–NSEC Memorandum of Understanding; proposed UK–EU Electricity Agreement; SSE Generation Ltd v CMA [2022] EWCA Civ 1472; BNetzA and Germany v ACER T-600/23 & T-612/23; TenneT TSO v ACER T-482/21; CRE v ACER T-446/21; Swissgrid v Commission C-121/23 P; and AEM C-128/03 & C-129/03. (EUR-Lex)