The U.S. State Department warned that the leaks would damage relationships around the world.
Spokesman P J Crowley said: ‘These revelations are harmful to the U.S. and our interests. They are going to create tension in relationships between our diplomats and our friends around the world.’
The U.S. ambassador to Britain, Louis Susman, was seen going into Downing Street and the Foreign Office yesterday to brief officials for what was described as ‘contingency planning’.
‘He came in to explain what they thought we could expect,’ said one Whitehall source.
Defence sources said British national security could be ‘put at risk’ by the release, as they are expected to contain details of the Iraq and Afghanistan conflicts and pull-outs and revelations about secret service practices and intelligence sources.
‘These revelations are harmful to the U.S. and our interests. They are going to create tension in relationships between our diplomats and our friends around the world’
Downing Street is braced for potentially hugely embarrassing disclosures about private U.S. assessments of Britain and its leaders.
There are fears of even the most apparently trivial secrets being hugely damaging.
One British official said they feared that mutual American and British contempt for the French would emerge.
‘Moaning about the French was practically a sport,’ he said.
Mr Cameron’s spokesman declined to discuss the nature of any confidential communications that could be released.
He said: ‘Obviously, the Government has been briefed by U.S. officials, by the ambassador. I don’t want to speculate about precisely what is going to be leaked before it is leaked.’
As well as Britain, the U.S. has warned the governments of Australia, Canada, Denmark, Norway and Israel in advance of the release.
Concern: Bombshell leaks are thought to include a U.S. assessment of Gordon Brown and David Cameron’s election chances – and secret talks on the return of Lockerbie bomber Abdelbaset Al Megrahi (right) to Libya
It has been claimed that a backlash by countries upset over the leaks may lead to U.S. diplomats being expelled.
The next release is expected to include thousands of diplomatic cables reporting allegations of corruption against politicians in Russia, Afghanistan and other Central Asian nations.
But there were no specific details as to the nature of the corruption allegations or which governments are involved.
However, according to the UK-based Arabic daily newspaper al-Hayat, the WikiLeaks release includes documents that show Turkey has helped Al Qaeda in Iraq – an extraordinary revelation which could kill off the country’s hopes of joining the EU.