It was suggested the President had already informed the Prime Minister of America’s reinforcement before Mr Brown made his Commons statement when he told MPs that the UK’s extra deployment “will be consistent with what the Americans decide”.

A surge of 45,000 would push the US force to over 100,000, although the White House was denying the reports last night.

Mr Obama convened his war council, coming under pressure to respond to a request from General Stanley McChrystal, the US and Nato commander in Afghanistan, for a significant surge to reverse the coalition’s flagging fortunes.

Mr Brown said he had made his decision to send more troops based on “clear military advice” but attached key conditions: an increase in Afghan troops to be trained; all British troops have the necessary equipment and there is increased burden-sharing by allies.

Given current and recent deployments, it is not thought the extra UK troops will be from the Royal Regiment of Scotland.

The PM said his government’s military strategy was “dedicated to counter insurgency” and so-called “Afghanisation”, accelerating the training of Afghan forces so the withdrawal of British ones can be brought forward.

He also made clear that to counter the threat from roadside bombs, new equipment, including mine-protected armoured vehicles, would be shipped out.

Earlier, the Commons took on a sombre atmosphere as Mr Brown began the first Prime Minister’s Questions of the autumn session by reading out the names of the 37 soldiers who died in Afghanistan over summer.

He said: “Nothing can erase the pain for their families. Nothing can be greater than the pride we take in their contribution to our country and our sadness at their loss.

“It is a day on which we put on record our gratitude and our commemoration of the sacrifice made by 37 of our armed forces serving our country in Afghanistan.”

Before the Commons announcement, Mr Brown came under fire from former defence secretary John Hutton who said it would have been “much more helpful” if the reinforcements had been sent six months ago.

Mr Hutton warned the Government could “screw it up really badly” if the forces were not given the resources they needed.