Defence Secretary Geoff Hoon today told MPs that Britain should agree to a United States request to use the Fylingdales early warning station for its controversial national missile defence system.

Mr Hoon said the Government had not yet formally replied to the US Administration following its request to upgrade the base on the North York Moors as part of its ''son of star wars'' project.

But in a Commons statement he added: ''Based on the analysis and discussion we have undertaken so far, I have come to the preliminary conclusion that the answer to the US request must be yes, and that we should agree to the upgrade as proposed.''

He said MPs would debate the issue next week, as part of a more general discussion on defence.

Attempting to calm local fears, Mr Hoon stressed that the American request did not mean ''some new massive construction''. It was simply a matter of upgrading computers within the top-secret base.

He also stressed that the upgrade should be seen in isolation.

''It does not commit us in any way to any deeper involvement in missile defence - although it gives us options to do so, should we decide on this at a later date.''

RAF Fylingdales has been a ballistic missile early warning system since 1963 and its golf ball-style radar domes were once a familiar landmark.

The US would use the upgraded base to track missiles fired at American targets, before, in theory, destroying them in mid-air.

The Defence Secretary said agreeing to the request ''will not significantly increase the threat to the UK''.

He told MPs that against the background of the ''marked increase in the potential threat to our security from weapons of mass destruction'' it was in the UK's national interest to help the US.

''From the UK's national perspective, this specific decision is one that has real potential benefits at essentially no financial cost,'' he said.

''But it will ensure that, if in the coming years we find that a potential devastating threat is becoming a reality, we have the opportunity to defend against it.''

Some Labour backbenchers and peace campaigners have warned against Britain becoming involved in the missile defence system, saying it contravenes ballistic missile treaties and would make Britain a target for rogue states.

Shadow defence secretary Bernard Jenkin broadly welcomed today's announcement, but he urged the Government to commit itself to full participation in the system. .