The European Commission has launched legal proceedings against the UK over nuclear inspections at Sellafield.
EU inspectors say access has been poor at the Sellafield plant
The EC will tell the European Court of Justice that Britain has not given it proper access over the past five years.
EU inspectors are required to check on material being stored in nuclear plants to ensure it is not being diverted from peaceful purposes.
The Department of Trade and Industry is studying the action but insists the dispute does not concern safety issues.
The EC said it was taking legal action "to demand that the British authorities comply with their responsibilities".
The dispute centres around access to an area of Sellafield nuclear plant know as "pond B30".
The pond contains fuel which corroded years ago while awaiting re-processing.
It is now in the form of a sludge, making it difficult to estimate the amount of material.
The lack of access makes it impossible for inspectors to check the actual amount of material stored against the official records, it is claimed.
Loyola de Palacio, the EC's vice-president responsible for energy policy, said several problems had arisen with the pond between 2000 and 2002.
Ms de Palacio says the government can still prevent legal action
She said: "In 2003 we held several discussions with the British authorities in order to receive a clear commitment from the UK government to show that it was dealing with relieving the problems in pond B30 and allow appropriate access to this pond.
"We have not been able to get this commitment from the UK government and we have not been able to get them to draw up a clear plan of action with a clear timetable with appropriate financial commitments which would back up the plan."
The Cumbrian nuclear re-processing plant was given until 1 June to come up with an accounting plan on how spent nuclear fuel has been processed.
Ms de Palacio claims that the UK government provided the EC with a "a draft that had not been approved by the British authorities so this is not a commitment at all".
But she said the legal action could still be stopped if the UK government provides the EC with the necessary commitments and access.
A DTI spokesman said the issues involved in the dispute with the EC were not connected to safety or environment-related controls.
He said: "The Euratom Treaty safeguards at issue here require the EC to satisfy itself that nuclear materials 'are not diverted from their intended uses as declared by their users'.
"Safety and environment-related controls fall within the remit of the Health
and Safety Executive and the Environment Agency."
Earlier this year, Sellafield was warned it could face stiff penalties for not meeting stringent EC rules on nuclear waste.
Under the 1957 Euratom Treaty it is up to EU inspectors to check accounting records of the nuclear material and compare them with the results of on-the-spot inspections.
The main purpose of such inspections is to make sure the nuclear material used is not diverted from peaceful and non-military uses.