Admiral Sir John "Sandy" Woodward also said that America now had little interest in supporting Britain in any conflict as a stable Argentina was more important to the State Department.

In a letter to The Daily Telegraph, Adml Woodward said Washington was pushing for negotiations over sovereignty and "significantly the islands are already being called the Malvinas by the US".

With the end of the Cold War and emergence of Asian powers Nato and Britain were not as important to Washington which in 1982 played a significant part in providing satellite intelligence and missiles to British forces.

"We can no longer rely on the Pentagon to support us in helping the islanders in their wish to remain essentially British sovereign territory," he wrote.

If as is likely significant oil reserves are found around the islands then pressure from Argentina will be immense to share in the riches.

President Barack Obama's administration also made clear in early 2010 that it would endorse calls for talks over the islands when it adopted the Organisation of American States useage of Malvinas instead of Falklands.

Adml Woodward said with the Armed Forces already "over-committed" in Afghanistan and Libya and the Navy drastically weakened following last year's defence review "the answer appears to be that we can do precisely nothing other than accede to US pressure".

The 79-year-old admiral led a substantial task force of two aircraft carriers, a dozen frigates and destroyers, four submarines and a total of 100 surface ships along with 25,000 servicemen were to retake the Falklands in 1982.

But the Royal Navy no longer has aircraft carriers, has lost its force of Harrier jump jets and seen its warship fleet cut in half over the last decade.

The islands are currently protected by a force of more than 1,000 troops with a reinforced company of infantry and four Typhoon fighters and a single frigate. However the Typhoons have no anti-ship or anti-submarine capability.

In a letter obtained by The Daily Telegraph last year Liam Fox, the Defence Secretary, warned the Prime Minister that the island's defences would become fragile in light of the looming cuts in the Strategic Defence and Security Review (SDSR).

He said axing the Nimrod MRA4 maritime reconnaissance aircraft would "limit our ability to deploy maritime forces rapidly into high-threat areas, and delete one element of our Falklands reinforcement plan".

The last of the £3.6 billion Nimrods was destroyed in March following the defence review.

A Ministry of Defence spokesman said: "Claims that the Falkland Islands could be taken without a fight are completely without substance. The current garrison in the Falkland Islands is much larger in scale and has a greater capability than in 1982 and this together with our ability to reinforce rapidly by air has been maintained. "

By Thomas Harding, Defence Correspondent
9:00PM BST 12 Jun 2011

Telegraph.co.uk