The EU executive brought a case to the European Court of Justice against Britain for failing to provide the Commission with a plan for the disposal of radioactive waste from the decommissioning of a reactor known as "Jason".

It is not the only dispute between Britain and the EU executive over nuclear-related issues.

Geelhoed's opinion came a day after the Commission launched a probe to check whether Britain's plan for a state-owned nuclear decommissioning body conforms with EU state aid rules.

Jason was a low power research and training reactor in the UK Department of Nuclear Science and Technology located at the Roval Naval College in Greenwich, southeast London. It was operated from 1962 to 1996.

The United Kingdom argued that the EU rules only applied to waste coming from nuclear plants operating for civil and commercial uses and it was therefore not obliged to provide the data.

Geelhoed's opinion concluded Britain had breached its obligations by failing to inform the Commission, but said states should be able to hold back under certain circumstances.

"In the case of each plan to dispose of defence-related radioactive waste, member states should be entitled to withhold information from the Commission only if they consider this absolutely necessary for the protection of their essential defence interests," he wrote.

Judges at the Luxembourg-based court will now begin deliberating. Decisions usually take three to six months after the opinion is given.