Whitehall sources confirmed last night that unofficial discussions were under way with the US over plans to base the rockets here as part of a "second front" of defence against missiles launched by so-called "states of concern" in the Middle East - Iraq, Iran and Libya.

"It is a natural development. It would be silly to think that will not happen," a Whitehall source said.

The plan shows that America's missile defence project has implications far beyond the use of the early warning radar station at Fylingdales on the north Yorkshire moors. A plan to base missile batteries here for a project which many in parliament and Whitehall believe is at best unnecessary and at worst dangerously provocative, would be even more controversial.

It raises the prospect of widespread opposition reminiscent of the nationwide protests that greeted the US deployment of cruise missiles in Britain and Germany during the cold war in the 1980s.

The Labour MP, Malcolm Savidge, a persistent opponent of the project, accused the government of planning to "squander vast sums of taxpayers' money on a scheme which is probably unworkable, against a very remote threat".

Russia yesterday warned that the American project would destabilise the world and and lead to a "new senseless arms race".

Geoff Hoon, the defence secretary, disclosed on Tuesday that he had received a formal request from Donald Rumsfeld, his American opposite number, to expand Fylingdales. Officials have indicated that Washington is also seeking bases for its missiles in countries in north-west Europe and that it was "reason able to assume" that Britain was a key part of its plans.

Mr Hoon has promised a full public and parliamentary debate on the Fylingdales request. A government decision to accede to the US request has been widely anticipated and has already provoked protests from Labour MPs and disarmament campaigners. It follows a recent visit to the site by the chief of the US missile defence agency, General Ronald Kadish.

Mr Hoon's statement on Tuesday made no mention of talks about missile bases in Britain.

A Ministry of Defence "public discussion" paper issued last week makes a number of references to the basing of missile interceptors in Europe.

It says that Fylingdales "could be a key building block for any future system of active missile defence protection for the UK and Europe. With interceptors placed somewhere in Europe, such a system could protect the UK and north-west Europe". It adds: "The US administration has on a number of occasions emphasised its keenness to involve its allies in a cooperative development programme expanded to cover US and European territory and beyond."

The MoD paper says the US intention is to "upgrade their missile defence capability every two years using the latest technology". It describes interceptor sites as a "key issue".

Mr Hoon said this week the government had a duty to assess the threat posed to Britain by ballistic missiles, possibly bearing chemical, biological or even nuclear warheads and that the issue was a matter of growing concern. But he said that "at present there is no immediate significant threat to the territory of the UK from ballistic missiles".

This assessment is at odds with that of Mr Bush who said on Tuesday that he was ordering the missile defence deployment to ward off "unprecedented threats" and to protect US citizens against "the catastrophic harm that may result from hostile states or terrorist groups armed with weapons of mass destruction and the means to deliver them".

In his letter to Mr Hoon, Mr Rumsfeld sought to win British support for missile defence plans by offering technology-sharing and commercial opportunities for British companies arising from research and development contracts. Mr Rumsfeld suggested British collaboration in other shorter-range missile defence projects.

On Tuesday, Mr Bush announced the deployment of 10 rocket interceptors at Fort Greely in Alaska by 2004, to counter perceived ballistic missile threats in the Asia-Pacific region, principally from North Korea. Mr Bush also ordered the construction of 10 rockets without indicating where they would be based, along with sea-based missile systems aboard Aegis destroyers, possible airborne laser weapons, and a network of sensors and satellites of which Fylingdales would form a part.

In Moscow yesterday, the foreign ministry said that it regretted "the activation of the attempt by the United States to create a so-called 'global anti-missile defence'." It added: "Now, after taking a political decision to deploy in 2004 several strategic interceptors with support from space, the
realisation of these plans has entered a new destabilising phase."