UK denies deal over Mururoa test data

British officials admitted yesterday that Britain, the US and France were co-operating on computer simulation techniques to predict the performance and reliability of nuclear weapons designs, but denied Britain had done a deal with France to obtain data from the controversial French nuclear tests in the Pacific.

Independent experts said direct data from the tests could be of value to Britain if there were plans to develop a joint British-French nuclear warhead - the "Eurobomb" - but not for purely British warheads, which were of a different design.

Last night the Labour defence spokesman, David Clark, said it would be in the British government's interest to end the speculation.

Dr Clark has written toMichael Portillo, the Secretary of State for Defence, demanding an explanation after suggestions, apparently from sources close to the Geneva negotiations on the Comprehensive Test Ban Treaty, of a "deal" between Britain and France to share test information. They said this might explain Britain's refusal to condemn the tests, which are vigorously opposed by many countries, including Australia and New Zealand.

Last night Dr Clark said he accepted the exchange of information might only relate to computer simulation and not to raw data from the tests, but demanded details about any co-operation. "It's quite clear they are receiving information as a result of the French test and the British people have a right to know," Dr Clark said.

The MoD said yesterday: "It is completely untrue to suggest the UK has acquired data from the recent French nuclear test, nor has France offered to provide us with data from this or any other test in the current programme. It is also untrue to suggest that we are contributing in any way financially towards the French nuclear programme."

The Foreign Office also said the claims were untrue. "The French have different weapon systems from us. That's why they're doing these tests. Otherwise they might expect to get information from the US."

Patricia Lewis, of the London-based Verification Technology Information Centre, said yesterday that there was a difference between sharing raw test data and possible co-operation on developing simulation techniques.

It is also believed that the main purpose of the French tests is not just to improve simulation methods but to prove at least two new miniaturised warheads before the test ban comes into force.

"I can't see how that data could in any way assist the UK," Dr Lewis said, "unless there is a joint warhead in the pipeline. There might also be a particular physics problem the UK may have which the French data may help."

MoD sources said the British already had reliable simulation methods, developed with the US and improved within the last month. "We are exploring with France and the US the possibility of collaborating under a Comprehensive Test Ban Treaty on ways of maintaining nuclear warhead capability and safety. Within that there's the simulation element. But it's very early days on that."

British and French experts meet in a joint Nuclear Commission to co- ordinate nuclear policy, but it does not discuss technical issues.