The head of the US missile defence project is to visit the UK base which is key to its success.
Defence chiefs have played down the significance of General Ronald Kadish's trip to the RAF Fylingdales early warning radar station, in North Yorkshire.
But it comes just three days after Defence Secretary Geoff Hoon signalled British participation in the controversial project.
Gen Kadish will visit on Wednesday after attending a conference on missile defence in London.
A Ministry of Defence spokewoman said: ''It is an informal familiarisation visit. It is not a pre-cursor to anything more serious.
''He asked to visit the base and it would be churlish, if not difficult, to refuse.''
Labour MPs have spoken out against the National Missile Defence programme.
Ministers insist they cannot even consider allowing the US to use the Fylingdales and Menwith Hill bases in North Yorkshire until a formal request is made.
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