By James Hamilton

The Barack Obama global roadshow swept through London yesterday with the US presidential candidate offering under-fire Gordon Brown some words of comfort.

After two hours of talks at Downing Street with the Prime Minister, the favourite for the White House said it was much easier to be popular before you were elected to power.

The Democratic senator also emphasised the importance of the so-called "special relationship" with Britain in dealing with global issues such as climate change.

Dozens of people gathered to chant his name outside the Downing Street gates and around Parliament where he spent a further hour with Conservative leader David Cameron.

But there was none of the "Obamania" seen in Germany when tens of thousands thronged the streets of Berlin to hear him make a keynote speech.

Obama, speaking to a huge crowd of journalists outside Number 10, said he had enjoyed "a terrific conversation" with Brown on the final day of his tour.

The US had a "deep and abiding affection" for Britain, he said, and was grateful for its "stalwart assistance" in Iraq and Afghanistan.

During his time with Brown he enjoyed a short walkabout near Horse Guards Parade, which sits behind the Prime Minister's residence.

After making the short trip to Parliament, Obama spent almost an hour - far longer than planned - talking in David Cameron's Commons office, first along with shadow foreign secretary William Hague and shadow chancellor George Osborne, and then one-to-one.

As well as detailed discussion of the economic crisis and foreign affairs, the pair chatted about the stresses of politics and the need for holidays.

The senator revealed he was going to take a week's holiday from the campaign in August and talked to the Tory leader about his plans for a family break in Cornwall.

Obama told the Tory leader that he had been advised by someone who used to work in the White House that, should he win, the most important thing to do was to devote "big chunks of time during the day when all you are doing is thinking".

Otherwise you "start to make mistakes or you lose the big picture", he said.

As the senator swept out through Parliament's gates it emerged that he was taking with him a box of CDs of music by some of Cameron's favourite British bands, including The Smiths, Radiohead, Gorillaz and Lily Allen.