Britain is facing pressure to expose anti-terrorist measures at the nation's nuclear plants to EU scrutiny as part of new stress tests in the wake of the Japanese radiation scare.
On the eve of talks between nuclear safety experts from EU member states, European Commission President Jose Manuel Barroso said he hoped for agreement on EU-wide test standards covering "natural and man-made scenarios".
But the UK is among some countries concerned about revealing the scope of the measures they have already taken to tackle any possible terrorist attacks.
EU governments agreed in March that, in the wake of the Japanese earthquake and resulting tsunami which overwhelmed the Fukushima nuclear plant, all 143 of Europe's own plants should undergo stress testing to common standards.
Now the details have to be worked out, with the UK unlikely to agree anything until publication of a Government report into domestic nuclear safety standards, commissioned before the Japanese crisis.
Authored by Chief Nuclear Inspector Dr Mike Weightman, from the Nuclear Installation Inspectorate, some findings are due out in an interim report next week, but Government officials insist current safety standards are already high.
They also warned that there could be difficulties agreeing common criteria covering sensitive details about anti-terrorist measures.
EU Energy Commissioner Gunther Oettinger, who will chair the meeting of the European Nuclear Safety Regulators Group, said in March: "We are creating a common European standard for tests for nuclear power plants."
He said the accord involved reassessing all potential risks - earthquakes, tsunamis, terror attacks, cooling systems and operational activities, hazards including power cuts, requirements for back-up systems, and design structures of nuclear power plants.
On Wednesday night President Barroso said in a statement: "The Commission is pushing to make sure that those who choose nuclear energy apply the highest possible standards of safety. Nuclear incidents ignore national borders. We must make sure that nuclear safety ignores those borders too."