The UK and US have held high level talks on the possibility of putting a "Son of Star Wars" anti-ballistic missile defence system on British soil.

An article in The Economist claims Prime Minister Tony Blair has lobbied President George Bush for the system.

But government sources have told the BBC that talks are "to keep Britain's options open", not a lobbying effort.

Russia has said the system, which tracks and destroys missiles launched at the US, will trigger an arms race.

Poland and the Czech Republic have both been approached by America about locating part of the hugely expensive system on their soil.

Secret talks

BBC Defence Correspondent Paul Wood said he had confirmed "secret high-level negotiations" had been taking place.

Talks were continuing between the National Security Council and Britain's top foreign affairs adviser Sir Nigel Sheinwald, he said.

But Downing Street has said talks are at a very early stage, and were intended only to keep Britain in consideration as plans were developed.

David Rennie, from the Economist, told BBC Radio 4's Today programme his understanding was that Mr Blair had "personally led" efforts for silos to be based in the UK, believing it would make Britain safer.

The system uses radar and satellites to detect enemy missile launches and to guide interceptors to their targets.

Shadow defence secretary Liam Fox said the Conservatives would not oppose locating part of the system in the UK, but wanted to examine it in detail.

'Get honest'

"We have had no details at all from the government despite asking a lot of questions in Parliament.

"If the government really do want to maintain what they regard as a bipartisan approach to defence in this country, they better start getting honest with the opposition," said Mr Fox.

Poland has recently confirmed the US wants to use its territory to build part of its missile defence base.

The US has also asked permission from the Czech Republic and received the backing of Czech Prime Minister Mirek Topolanek.

In 2002, the US withdrew from the 1972 Anti-Ballistic Missile Treaty it signed with the Soviet Union.

It says a missile defence system could significantly reduce threats from so-called "rogue states" such as Iran and North Korea.

But Paul Ingram, of the British American Security Information Council, said the success of the system was "a long way from being proven".

"Even if it did work, it would be tackling the wrong problem at the wrong time," he told the BBC.

"The proliferation of ballistic missile technology is not as racing away as we are being led to believe. It has no relevance at all when it comes to issues like the war on terror."