Downing Street has played down newspaper reports suggesting that Gordon Brown could quit British politics to become the new head of the International Monetary Fund.

According to the Guardian, the chancellor is being considered for the top post by officials at the IMF's Washington headquarters.

Downing Street played down the significance of the story and paid tribute to the chancellor.

The official spokesman accepted the IMF role was a "big job" but pointed out the Brown already had a big job.

The vacancy has arisen because Horst Kohler resigned with immediate effect on Thursday to seek the German presidency.

In post since 1997, Brown has already become the longest serving Labour chancellor.

But by taking the five-year post at the IMF, he would be effectively ruling himself out as Tony Blair's successor as prime minister.

Despite that, one insider was quoted as saying that Brown would not "dismiss things out of hand".

"If it was offered, he would have to think about it seriously," said the source.

"I hope that Tony will decide to retire from that job in the next year or so because I think that Gordon would do it very well," he told BBC News 24.

"He [Brown] hasn't got the charisma of Tony Blair but he does at least now start smiling, because ever since he met Sarah, and it is particularly since they had a child, I think he smiles a great deal and he's a very attractive man, a very nice man.

"If you stay in the same job too long I think you tend to get too fixed in your manner of dealing with problems and it's time for a change in that sense and I think that Gordon would do it very well."