PM warned over 'untested' Obama

Sir Nigel Sheinwald sent a letter to the Prime Minister which said the Democratic presidential nominee was someone who was still "finding his feet" when he "got diverted by his presidential ambitions", the Daily Telegraph reported.

The British Ambassador called Mr Obama "elegant", "mesmerising", and "highly intelligent" but added that, if elected, he would "have less of a track record than any recent president".

The seven-page letter was reportedly sent to Mr Brown on the eve of Mr Obama's visit to London in July.

"Although he has been a member of the Senate Foreign Relations Committee for four years, and a regular attender of meetings in his first two, there is little Obama track record to refer back to," the letter said.

Sir Nigel also warned the Prime Minister that Mr Obama's stance towards Iran may conflict with the United Nations Security Council's demands that the country stop enriching uranium before negotiations resume.

But the ambassador seemed to approve of Mr Obama's policy in Iraq. "Whatever the detail, our own proposed transition in south-east Iraq would be consistent with Obama's likely approach," he was quoted as saying.

The British embassy in Washington declined to comment on the report.

Last month, Mr Brown was accused by the Tories of taking sides in the elections after he praised the Democrats and cited one of presidential hopeful Barack Obama's proposals to help families in a magazine article. He did not mention Republican rival John McCain.

Mr Brown later attempted to defuse the row by stressing his "admiration" for both candidates.