Just as John McCain pulls ahead in the US presidential race, Gordon Brown has decided to throw his weight behind Barack Obama.

Or, at least, that's what it looks like for the McCain campaign.

Downing Street hastily denied Tory accusations today that the Prime Minister was taking sides in the race for the White House after he showered praise on Mr Obama, the Democratic candidate, in a magazine article. Traditionally, foreign leaders try to maintain a scrupulous neutrality during election contests.

Writing in the Parliamentary Monitor, a Westminster magazine, Mr Brown said that the Democrats were the party in America who were developing ideas to help people through the current economic difficulties and cited one of Mr Obama’s proposals to help families facing repossession.

“In the electrifying US presidential campaign, it is the Democrats who are generating the ideas to help people through more difficult times," he said. “To help prevent people from losing their home,

Barack Obama has proposed a Foreclosure Prevention Fund to increase emergency pre-foreclosure counselling, and help families facing repossession.”

The article did not mention Mr McCain, the resurgent Republican candidate but it was reported a member of Mr McCain’s campaign team contacted the British Embassy in Washington DC to express concern about the article.

William Hague, the Shadow Foreign Secretary, said that the Prime Minister should not do anything which suggests he is taking sides, as he will have to work with whichever candidate wins November’s election.

He said: “A responsible British Prime Minister needs to be ready to work with either presidential candidate after the US election, and should neither take sides nor be seen to be taking sides. Gordon Brown needs to make clear why he appeared to be favouring the Democrats in this article and to explain whether this was his deliberate intention or a careless mistake.”

Downing Street denied that Mr Brown was taking sides in the US election. A No 10 spokesman pointed out that Mr Brown had met Mr McCain both in London and the United States this year, just as he has met Mr Obama.

“The PM is not endorsing a candidate, and never would,” said the spokesman.

“As he has made clear when asked on a number of occasions, the election is a matter for the American people, and he looks forward to working closely with whoever is the next President across a range of areas of common interest.

“This was an article written ahead of the party conferences in Britain and talks about some of the measures being taken around the world by centre-Left political parties to deal with the current global economic challenges.”

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