The British National Space Centre (BNSC) is believed to have said that the plan, which might cost £100m and lead to a British astronaut flying aboard the ISS, is not worth the money.

The science minister, Lord Sainsbury, is believed to broadly agree. If the government takes the BNSC's advice, Nasa and the European Space Agency are likely to be angered.

They have lobbied hard for Britain to get involved, particularly as the Russian economic crisis threatens that country's involvement.

Not value-for-money

Paul Murdin is BNSC's Director of Science and told the BBC in an earlier interview: "I said that we have decided that the ISS is not worth it on a value-for-money basis." But he added that if the government had political reasons for joining, then they should.

Gary O'Donoghue reports on Britain's ISS plans

A spokesman for the BNSC told BBC News Online that it had given advice on the cost implications of both joining and not joining the ISS and that it was now up to the government to decide.

He said that the BNSC's annual budget of £200m was already committed to work in the UK and with Nasa and ESA - any ISS involvement would require new funds.

The story so far: two ISS modules have been joined

The $40bn ISS is the most complex and expensive engineering project ever attempted. Sixteen countries have been involved, but not Britain, which passed up the opportunity to take part in 1987.

For the past few months, Lord Sainsbury has been reviewing that decision and his report is now with the Prime Minister Tony Blair.

Space scientist Dr Martin Barstow at Leicester University believes Britain cannot afford not to be involved: "I would be really disappointed by that decision. We do a lot of our space science in collaboration with Nasa and ESA and if opportunities for doing new missions are linked to the ISS, but we are not involved, that will create serious difficulties."

Franco Bonacina of ESA says not being involved could affect British jobs: "By investing more and more in space activities, there are more and more contracts which benefit the industry of the member states. The more you invest, the more the return is, in the end making work for people."

Ego boost

However, the man who decided to keep the UK out in 1987, is not convinced of the benefits. Former Chancellor of the Exchequer, Kenneth Clark says: "It is largely about good television. It is mostly done for national prestige and to boost the egos of ministers who associate themselves with the project."