Ministers were today urged to consider abandoning the multi-billion pound Joint Strike Fighter project unless the United States agrees within weeks to share sensitive technology.

The Government should develop a "plan B" for jets to operate from two new aircraft carriers if a deal is not struck by the end of the year, according to the influential Commons Defence Select Committee.

Progress on the £140 billion project - the most expensive single armaments programme in UK military history - has been dogged by wrangles over whether Britain would be given access to the technology powering the high-tech aircraft.

Ministers have previously threatened that the UK could pull out of plans to buy up to 150 of the military planes for the RAF and Navy unless America agreed to transfer secrets about its software that Britain argues are needed in order to operate and maintain them independently.

It appeared that Tony Blair and George Bush had solved the impasse in May, when they announced an agreement in principle that the UK would be given access to the classified details on conditions of strict secrecy.

The news was widely seen as evidence that the Prime Minister’s close alliance with the American President did have benefits for Britain.

But in a report on defence procurement published today, the committee warned that it was still "uncertain" whether the US was prepared to supply the required information.

"If the UK does not obtain the assurances it needs from the US then it should not sign the Memorandum of Understanding covering production, sustainment and follow-on development," the MPs insisted.

The report said that backing off from the deal would constitute a "serious blow" to defence co-operation between the UK and America, but other options had to be considered.

"If the required assurances are not obtained by the end of the year, we recommend that the Ministry of Defence switch the majority of its effort and funding on the programme into developing a fallback ‘plan B’, so that an alternative aircraft is available in case the UK has to withdraw from the Joint Strike Fighter programme.

"We must not get into a situation where there are no aircraft to operate from the two new aircraft carriers when they enter service," the MPs added.

The Committee also expressed "concern" that delays in production of the aircraft could lead to an increase in cost of between 25 per cent and 35 per cent.

Aside from the JSF project, the MPs also looked at procurement for the ongoing military operations in Afghanistan and Iraq. They said that despite the Prime Minister’s recent commitment to provide all equipment requested by commanders on the ground there were still worrying shortages.

The report identifies a lack of heavy lifting aircraft as a particular problem, and describes the "sorry episode" of eight Chinook Mk3 helicopters which remain in British hangars while the MoD negotiates with manufacturer Boeing over responsibility for solving a software issue.

The negotiations could go on until "the next decade", and the incident is estimated to cost the taxpayer £205 million, according to the MPs.

Gerald Howarth, Shadow Defence Minister, said: "The Government has failed to deliver the essential equipment needed by our Armed Forces when Britain’s military commitments are increasing.

"Whilst Gordon Brown this week may have promised an additional £600 million to the military, it is too little, too late."

He added that the Tories endorsed the Government’s call on the US to secure the transfer of technology and Britain might have to find an alternative fighter.

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