A British defense minister arrives in Washington today in an attempt to save a collaborative deal with the United States on the $256 billion Joint Strike Fighter, the most expensive military programme in history.

The visit by Lord Drayson, the Minister for Defence Procurement, comes before a looming Dec. 31 deadline for Britain to sign up for the next stage of the proposed new jet aircraft’s development.

Britain has threatened to pull out of a planned $19.5 billion purchase of the new fighters if the U.S. refused to share secret computer technology needed to maintain operational sovereignty over the Armed Forces.

The Pentagon plans to manufacture 2,500 F35s. The aircraft is expected to make its maiden flight next week in Texas.

Although Tony Blair believed that he had brokered an agreement with President Bush on a trip to the US in May, the dispute has dramatically reignited in recent days as the deadline approaches.

British officials have told The Times of London that in the seven months since there has been “no breakthrough — or even any sign of one — because the Americans have been preoccupied by Iraq and the midterm elections”.

The row comes at a sensitive time for transatlantic relations, with Mr. Blair being widely seen as having sacrificed his political popularity at home and tarnished his legacy through his unconditional support for the war in Iraq. Kendall Myers, a senior analyst at the U.S. State Department, recently described the relationship as “totally one-sided” with no “payback” for Britain at all.

Lord Drayson has considered a number of “Plan B” options for replacing Britain’s aging Harrier ground-attack aircraft if the deal for buying about 150 Joint Strike Fighters falls apart. These are thought to include buying French Rafale jets, which can fly from aircraft carriers, or more Eurofighter Typhoons.

If the Britain went down the French or European route, it would be seen as hugely damaging to the so-called special relationship, in which the ties that bind Britain and America together are increasingly defence-related.

“If we can’t trust the Americans to provide this, then you would have to ask what else we should be doing with them in defence terms,” a Ministry of Defence source said. He confirmed that it would also raise questions over the deal under which Britain needs U.S. help to replace its Trident nuclear missile system.

A report last week by the Commons Defence Committee said that it was still uncertain whether the U.S. was prepared to supply the required computer codes for the new fighter.

“If the UK does not obtain the assurances it needs from the U.S. then it should not sign the memorandum of understanding covering production, sustainment and follow-on development,” the MPs insisted.

Instead, they recommended that the MoD “switch the majority of its effort and funding on the programme into developing a fallback Plan B [because] we must not get into a situation where there are no aircraft to operate from the two new aircraft carriers when they enter service."