Britain's military cuts mean it will no longer be able to be a full partner alongside United States forces, former US defence secretary Robert Gates said Thursday.
Gates, who served under US presidents Barack Obama and George W. Bush, said Britain no longer had the complete spectrum of capabilities, meaning its relationship with the US military was shifting.
The comments suggest Britain's military downsizing could have a negative impact on the "special relationship" between Washington and London.
Gates, speaking to BBC radio, highlighted the Royal Navy's lack of an aircraft carrier able to launch strike jets.
"What we have always been able to count on, on this side of the Atlantic, were British forces that had full spectrum capabilities very much along the lines of our own forces, that they could perform a variety of different missions," Gates said.
"With the fairly substantial reductions in defence spending in Great Britain what we are finding is they won't have full spectrum capabilities and the ability to be a full partner as they have been in the past.
"I also lament that reality."
Prime Minister David Cameron's coalition government announced heavy defence cuts in 2010 as part of its bid to rein in Britain's massive deficit.
The defence budget is being slashed by eight percent over four years.
Between 2010 and 2020, Britain is reducing the size of its regular military from 178,000 to 147,000, while boosting the number of reservists.
Britain has three helicopter landing craft: HMS Illustrious, Ocean and Bulwark.
However, it will not have carrier strike capability until the new aicraft carrier Queen Elizabeth -- which will be Britain's biggest-ever ship on the seas -- enters service in 2020 with F35 fighter jets.
Gates said of the lack of carrier strike capability: "Those kinds of things, I think, at the end of the day matter."
This century, Britain has been the United States' closest partner in the wars in Iraq and Afghanistan.
"Our primary partner for many decades now has been the United Kingdom.
"I would a lot rather, in a port in the Middle East, have a British-flagged ship and an American-flagged warship than just an American-flagged warship by itself."
He also urged Britain to renew its nuclear deterrent.
The coalition has deferred a decision on replacing Britain's nuclear weapons programme -- the Trident missile-based system on board its submarines -- until after the 2015 general election.
"As we reduce the size of our nuclear arsenal we potentially get down to numbers that having allies who have their own capability could be very helpful," he said.
"I think it's important for the UK not to deny itself this military capability altogether."
A Ministry of Defence spokesman said: "Like the United States, the UK has had to take tough decisions on defence spending, but we still have the fourth largest defence budget in the world and the best-trained and best-equipped armed forces outside the United States."