The agreements cover America's use of an upgraded early warning radar station at Fylingdales on the North York Moors and unspecified "technical cooperative programmes".

They also include what Geoff Hoon, the defence secretary, described to MPs yesterday as an agreement which "prepares the way for fair opportunities to be given to UK industry to participate in the US programme".

Mr Hoon insisted that none of the agreements committed Britain to the "acquisition or deployment of a missile defence system". He described the agreements as "an important step forward" which would enable Britain to "improve our understanding of the capabilities of the US system... to inform any future decisions on missile defence for the UK or Europe as a whole".

The project is being pushed by Donald Rumsfeld, the US defence secretary, who says it is needed to counter threats from "rogue states" such as North Korea.

Critics are likely to seize on the agreements as further evidence that the government is committed to supporting the US project.

Menzies Campbell, the Liberal Democrat foreign affairs spokesman, criticised the secrecy surrounding the deals. "What the UK needs is not another confidential agreement with the US on missile defence but an international and multilateral approach to the issue," he said.