Downing Street has given an agreement in principle to the Pentagon to station interceptor missiles at RAF Fylingdales, North Yorkshire.

The confidential deal goes far beyond the official position that Britain is providing enhanced radar provision for the US national missile defence programme.

News of the deepening collaboration over the missile defence programme comes as the Prime Minister considers an American request to send British troops to the US-controlled sector of Iraq.

There was growing anger last night that UK soldiers stationed in Iraq might be put in even greater danger than they are already just to assist a pre-election offensive ordered by the Bush administration.

The siting of the interceptors on British soil would represent the most significant new military US presence in this country since the withdrawal of cruise missiles 13 years ago.

If re-elected, President Bush has pledged to spend around $10bn (£5.5bn) a year on realising Ronald Reagan's dream of erecting a missile shield to protect the West from long-range attack.

Sixteen interceptor missiles are being positioned in bases in Alaska and California this year. The intended location of the remaining 24 is a closely guarded secret, although it is known that the Pentagon wants to site some in Europe.

Mr Blair and Geoff Hoon, the Secretary of State for Defence, refuse to be drawn on how far Britain is prepared to co-operate in the programme, insisting that the US has made no formal request to site missiles here.

This newspaper has learnt, however, that an offer to site missiles in Yorkshire was made in a meeting in Washington in May this year and that preparations are well under way to overcome public and parliamentary opposition.

The meeting, one of a series held to discuss US-UK collaboration on the programme, was attended by senior officials from the British embassy, a deputy to John Bolton, the Pentagon's secretary for arms control, and staff from the US State Department.

British diplomats gave an agreement "in principle" to siting interceptors at RAF Fylingdales, but asked that no formal request be made until after the next general election.

Ministers are confident they can win public support for the missiles. They will insist that Britain has ensured the US respects two "red lines": that the system must be strictly defensive and that it must cost the British taxpayer nothing.

Mr Blair intends to argue that Britain has been given an extra line of defence from nuclear attack at no extra cost.

He will also point out that Britain is not alone in offering to site the interceptors. A number of Eastern European countries have indicated willingness, with Poland considered the leading contender.

A Ministry of Defence spokesman said: "The UK has not yet decided whether we need our own missile defence. This is a decision for the future when the US system has further evolved."

The prospect of a confidential agreement on missile defence between Mr Blair and Mr Bush has appalled opposition and Labour MPs.

Sir Menzies Campbell, foreign affairs spokesman for the Liberal Democrats, said: "These reports, if true, are a source of grave concern given that a decision appears to have been taken behind closed doors before a full public debate on the costs and strategic implications.

"This could have major implications for the defence posture of the UK, our relationship with Nato countries and other allies, and the strategic balance of nuclear weapons around the world."

Sir Menzies also expressed concern that a formal agreement between Britain and the US on "co-operation, development, test and evaluation activities related to missile defence" has not been released.

Mr Hoon said he would be placing a copy in the Commons library on Tuesday. There was no sign of it as of Friday afternoon, however.

"In view of the potential significance of these events it's extraordinary that MPs don't yet have access to this agreement," Sir Menzies said.

Malcolm Savidge, MP for Aberdeen North and a leading opponent of missile defence, said it would lead to a revolt among Labour backbenchers. "This is part of an increasing surrender of British interests to satisfy the obsessions of the Bush administration."

Critics of ballistic missile defence argue that it will lead to a new arms race as nuclear-armed states build faster, more powerful missiles to evade the defensive systems.

The Ministry of Defence has confirmed that it has signed a £30m agreement to help develop and test a new generation of ballistic weapons, dubbed 'son of Star Wars' and designed to intercept attacks from rogue states and terrorist groups.

But in an even more significant move, it is understood the Prime Minister has given his consent 'in principle' to the siting of American missile interceptor batteries in Britain, probably at Fylingdales in North Yorkshire.

The move would represent a drastic shift in Britain's approach to the Star Wars missile shield initiative, which has provoked furious opposition from campaigners who believe it will accelerate the arms race and make the UK a target for attack.

When Bush's plans were first announced, the US government asked if it could use the facility at Fylingdales simply as part of the radar network upon which Star Wars depends. Defence Secretary Geoff Hoon indicated he was prepared to grant the request.

But the new plan goes much further, placing controversial American military hardware on UK soil while including Britain in its protective umbrella.

It would also put Blair on a collision course with Nato allies and many of his own MPs, as the final decision to allow the Americans to site missiles in the UK would have to be ratified by Parliament.

Sir Menzies Campbell, the Liberal Democrats' foreign affairs spokesman, last night warned that news of progress on transatlantic co-operation on New Missile Defence (NMD) was "a source of grave concern".

He added: "This could have major implications for the defence posture of the UK, our relationship with Nato countries, and other allies and the strategic balance of nuclear weapons around the world."

President Bush has invested billions in developing the missile shield, first proposed by his predecessor Ronald Reagan at the height of the Cold War in the 1980s. The Pentagon is siting 10 missiles in Alaska and California this year.

But the Americans remain keen to extend their shield further afield, preferably into Europe. The UK is their favoured location. Britain signed a secret "framework agreement" last year, paving the way for greater transatlantic co-operation on missile defence, and setting out the rules governing America's access to an upgraded early-warning radar station at Fylingdales.

Ministers expect a similar request for the US to use the "spy station" at nearby Menwith Hill to support the scheme.

But last week, while attention was focused on further revelations about the use of intelligence before the war on Iraq, Geoff Hoon confirmed the government had now fully signed up to a detailed agreement, which effectively moved Britain closer to assuming the protection of the Star Wars shield.

"The MoD has signed an agreement setting out mechanisms for co-operation with the US in research, development, test and evaluation activities related to missile defence," the Defence Secretary revealed in a written statement to MPs.

"This agreement replaces the 1985 strategic defence initiative memorandum of understanding as the vehicle for co-operation between the UK and US in the field of missile defence.

"It is intended that the new agreement will improve co-operation by providing information transfer and contracting mechanisms in keeping with current US and UK practices and the current state of development of the US missile defence capability."

The Pentagon has refused to disclose its favoured location for the next 30 interceptor missiles, but Scotland on Sunday understands that a number of European countries, including Poland and the Czech Republic, have indicated a willingness to host the batteries on their soil.

Blair is now believed to have agreed to similar proposals, although he will maintain that any siting of US missiles in this country would be within strict parameters.

In a little-noticed written statement to the Commons last week, the defence secretary, Geoff Hoon, said a copy of a new memorandum of understanding on the "Son of Star Wars" programme was being put in the Commons library but with parts missing after a US request.

Britain is allowing the US to upgrade the early-warning radar station in Fylingdales, North Yorkshire, and to extend the US satellite ground station at Menwith Hill, in the same county, to play a part in tracking missiles.

US and British officials have been discussing the deployment of US interceptor missiles in Britain. The Ministry of Defence yesterday denied receiving an approach from the US, but it is understood that the countries have agreed not to announce any provocative move until after the British election.

British diplomats in May agreed "in principle" to allow the U.S. missile-defense interceptors to be installed at Fylingdales Royal Air Force base in North Yorkshire, the Independent reported. British officials, however, denied that the United States has made any formal request regarding interceptors.

"The U.K. has not yet decided whether we need our own missile defense," a Defense Ministry spokesman said. "This is a decision for the future when the U.S. system has evolved further."

The Independent, however, reported that diplomats requested that a formal request be made only after the next British general election (Elliott/Carrell, London Independent, Oct. 17).

"[I] have never heard anything regarding basing interceptors in U.K. MDA's only role is upgrading the Fylingdales early warning radar for integration into the [Ground-based Midcourse Defense] system next year," he wrote in an e-mail (see GSN÷ Feb. 6, 2003).

Nigel Chamberlain of the British American Security Information Council in London said that Fylingdales would not be a likely site for basing the missiles.

"My understanding is that the issue of basing an interceptor battery in the United Kingdom has been raised but that any potential site is more likely to be an existing military base, other than on Fylingdales Moor in Yorkshire," said he said (David Ruppe, Global Security Newswire, Oct. 18).

Opposition politicians and members of Blair's own Labor Party expressed strong reservations about the reported agreement, the Independent reported.

"These reports, if true, are a source of grave concern that a decision appears to have been taken behind closed doors before a full public debate on the costs and strategic implications," said Menzies Campbell, foreign affairs spokesman for the Liberal Democrats. "This could have major implications for the defense posture of the U.K., our relationship with NATO countries and other allies, and the strategic balance of nuclear weapons around the world."

In seeking political and public support for the plan, British leaders will stress to their U.S. counterparts that the system must be strictly defensive and be installed at no cost to the United Kingdom. Blair is expected to note that the island nation has received an added defense, free of cost.

Poland and other Eastern European countries have already expressed interest in housing missile interceptors (Elliott/Carrell, London Independent).

The next British general election is expected to be held in May 2005, the Press Association reported (Gavin Gordon, Press Association/Scotsman.com, Oct. 17).

Details of the agreement were to be included in a memorandum of understanding to be placed in the British House of Commons library, the London Guardian reported today. Defense Minister Geoff Hoon said parts of the memo were missing at the request of U.S. officials (Richard Norton-Taylor, London Guardian, Oct. 18).