The US is about to ask Britain if it can use the Fylingdales radar station in North Yorkshire for its controversial national missile defence system, the BBC has learned.

Senior Ministry of Defence sources have told the BBC the request is expected as early as next week.

The sources said they would consider the request, for the so-called Son of Star Wars programme, very carefully.

The defence minister said the UK would only agree to this if it was in the best interests of the UK MoD

A spokeswoman later said that if such a request was made, it was by no means a foregone conclusion that Britain would acquiesce.

"The defence minister said last week in Parliament that the UK would only agree to this if it was in the best interests of the United Kingdom."

The government faces some opposition to the move, with many of its own backbenchers against the idea.

Fylingdales has an advanced radar which could track missiles launched by rogue states or terrorists in, for example, the Middle East.

They would then in theory be shot down as they neared the US coast.

Opponents say the scheme is unnecessary, would not work and would simply make Britain a target - without giving it a protective screen of missiles.

I think that the system itself is doubtfully technically feasible; it potentially undermines arms controls Malcolm Savidge Labour MP

Labour MP Malcolm Savidge demanded a Commons debate on whether Britain should participate in US plans for the system.

He told BBC Radio 4's Today programme: "I think this is a very dangerous system in a number of ways.

"I think it is set up against a risk which is a very low one; I think that the system itself is doubtfully technically feasible; it potentially undermines arms controls."

Former defence minister Peter Kilfoyle, Labour MP for Liverpool Walton, said he suspected the request for the use of Fylingdales was being timed to coincide with a parliamentary recess due next week.

Liberal Democrat defence spokesman Menzies Campbell told Today he would agree to the base's use, but only with conditions.

He said it should be demonstrated that "the use of Fylingdales will increase not only the security of the US and the UK, but the security of all of our Nato allies and all of our EU partners".

'Familiarisation' trip

The government has recently been making pro-missile defence statements - prompting most commentators to suggest a "no" is unlikely.

Last week, it published a report arguing that taking part in US missile defence plans would not immediately put the UK itself at greater risk of attack.

Defence Secretary Geoff Hoon has previously told MPs the UK would consider "very seriously" any US request to use Fylingdales for a missile defence project.

And last month the US head of the Son of Star Wars project, Lieutenant General Ronald Kadish, visited the site on a "familiarisation" trip.

Conservative shadow defence secretary Bernard Jenkin has described the UK's agreement as a foregone conclusion, branding any show of government public consultation a "charade".