Obama meets Brown at Downing Street

But he said: “You’re always more popular before you’re actually in charge. Once you’re responsible then you’re going to make some people unhappy.”

Mr Obama said he and Mr Brown had talked about strengthening the relationship between the US and Britain.

He said he had thanked Mr Brown for Britain’s “stalwart assistance” over issues such as Afghanistan and knew British troops had “borne a heavy price”.

The Democrats’ candidate said he has already committed to increasing the number of troops in Afghanistan if he is elected.

But he hinted that Britain would also be expected to offer support when he added: “We’d like that burden shared.”

Mr Obama said there had been times during the Democratic Party primary campaign when his popularity had been at a low ebb and he had been criticised by the media.

“There have been months when I’m a genius and months when I’m an idiot if you read the newspapers.

“It seems (to me) I’m pretty much the same guy during this process.”

The Illinois senator spoke to dozens of reporters, television cameras and photographers amassed outside No 10.

As he spoke a small crowd gathered at the gates of Downing Street chanted his name.

He said his meeting with Mr Brown had been “wonderful” and said the two leaders discussed how to strengthen the transatlantic relationship on issues such as climate change, international terrorism and financial markets.

He said the relationship was important “to solve problems that can’t be solved by any one country”.

He added: “I’m looking forward to the possibility of seeing the United States and Great Britain taking the lead.”

Asked if there was a special relationship between the US and the UK he replied: “Absolutely”.

“I expressed gratitude for Great Britain’s stalwart assistance on issues like Afghanistan,” he said of his meeting with Mr Brown.

“I know the troops here in Great Britain have borne a heavy price.

“I think the American people are grateful.”