The US administration's unflattering assessment of British Prime Minister David Cameron is set to be made public with the release of thousands of leaked State Department files by the WikiLeaks whistleblowers website.
Simon Hoggart, a journalist on The Guardian - one of the newspapers that has been working with WikiLeaks on the release of the material - said that the publication would be an "embarrassment" for Cameron.
He confirmed that the paper would be releasing extensive details of the files tomorrow.
"It is going to give the candid American views of world leaders and indeed the reverse too," he told BBC1's 'The Andrew Marr Show'.
"There is going to be some embarrassment certainly for Gordon Brown but even more so for David Cameron who was not very highly regarded by the Obama administration or by the US Ambassador here."
The US administration has warned that the release of the files would put "countless" lives at risk, threaten global counter-terrorism operations and jeopardise America's relations with its allies.
The State Department's senior lawyer Harold Koh has written to WikiLeaks founder Julian Assange, warning that the publication could do massive harm to America's standing by exposing secret military operations.
Mr Koh sent the message in response to a letter from Mr Assange and his lawyer in which they asked about the safety of people who might be named in the files. Mr Koh said that the US would not co-operate or negotiate with WikiLeaks.