American visitors to Britain have a reputation for whirlwind “if-it’s-Wednesday-it-must-be-London” tourism. But none can ever have had a schedule as breathless or as daunting as that of President Obama yesterday.

Dragging his vast global agenda around the streets of the capital, he had breakfast at Downing Street followed by a full press conference alongside Gordon Brown, before embarking on a momentous first meeting with the President of Russia — resetting relations with America’s old Cold War adversary — and what may turn out to be equally important talks with the emerging economic rival of China.

Then there was tea with the Queen followed by a reception at Buckingham Palace and, finally, a dinner back at No 10 for G20 leaders.

Somehow, he also managed to squeeze in 30 minutes for David Cameron, a telephone call with the Israeli Prime Minister Binyamin Netanyahu to congratulate him on his inauguration, and even a chat with Mr Brown’s children about dinosaurs.

As his motorcade tracked back and forth between Westminster, the American Ambassador’s residence at Winfield House and the Palace, Mr Obama avoided the protests designed to strangle the City yesterday.

From the window of his armoured limousine he would have seen only clumps of admiring onlookers enthralled with this new President — and the gaze of the world still hanging on his every word.

Mr Brown could scarcely contain himself as he clung to Mr Obama’s coat-tails yesterday, congratulating him on “the dynamism, the energy and, indeed, the achievements that you have been responsible for” in 70 days of office that have “changed America . . . changed America’s relationship with the world”.

The President’s popularity in Downing Street and on the streets is derived, at least in part, from the scale of his ambition. If the economy undoubtedly looms largest before today’s summit, his discussions yesterday ranged across a bewildering array of global challenges including nuclear disarmament, Afghanistan, Iran, North Korea, the Middle East peace process, climate change, human rights, development goals and terrorism.

Either one of his meetings with President Medvedev of Russia and President Hu Jintao of China would usually have been notable enough to dominate the news for a week. That Mr Obama managed these so within hours of a testing press conference with Mr Brown to soothe ruffled sensibilities about Britain’s place in the world — even while preparations for a crucial G20 meeting continued — was a breathtaking display of audacity bordering on the hubristic. “We don’t do drive-by summits,” boasted an adviser, “we have meetings of substance.”

Little local difficulties such as a threatened walkout from the summit by President Sarkozy of France seemed to pale in comparison. Mr Obama airily dismissed as “arguing at the margins” all the reports of rifts with the leaders of France and Germany. “I know that when you’ve got a bunch of heads of state talking, it’s not visually that interesting,” he said, “so there’s a great desire to inject some conflict and some drama into the occasion. But the truth of the matter is . . . that I think there has been an extraordinary convergence.”

As one exhausted member of his team told The Times: “Believe me, there is enough other stuff out there to focus on.” And yet, as Mr Obama fights on a dozen different fronts, the erosion and limitations of America’s global dominance are being exposed by an economic crisis that much of the world blames on the reckless behaviour of its financial institutions.

Mr Obama is aware that the ability of the US to impose a new economic order on the world, as it did after the Second World War, is already constrained by the growing financial muscle of countries such as China, which is seeking to buy its way into the exclusive club of nations controlling institutions such as the International Monetary Fund. Exactly how much China will pay for such influence was one of the chief subjects discussed between Mr Hu and Mr Obama yesterday.

The US also needs help to tackle myriad security threats. The tentative agreement that he reached with Mr Medvedev yesterday on the need for a new treaty for cutting nuclear warheads is, the White House hopes, the start of deeper co-operation on shared challenges facing both nations, including the unfinished war in Afghanistan and the nuclear ambitions of Iran.

Mr Obama has long since blamed the military adventures of the Bush Administration for damaging America’s moral authority and standing in the world, but this week he has acknowledged that many other countries are now less inclined to follow a US lead on economic matters after being lectured for so long on copying its preferred model of deregulation.

The demonstrations in London are part of a pattern of protests across Europe in recent weeks aimed at the capitalist free markets and forces of globalisation which for so long sustained US economic hegemony. President Lula da Silva of Brazil said last week: “This is a crisis that was caused by white people with blue eyes,” who thought that they “knew everything about economics”.

Mr Obama has arrived in London showing a degree of humility which the White House regards as the “price of admission” if America is to command the stage once more. “I came here to put forward our ideas, but I also came here to listen, and not to lecture. Having said that, we must not miss an opportunity to lead,” he told the press conference. At one point the President even described the US as “a peer to these other countries” in the G20 — a statement that would until recently have been unthinkable — and recognised that it “certainly has some accounting to do with respect to a regulatory system that was inadequate”.

Although he insisted that reports of America’s decline were exaggerated, Mr Obama said: “There is no doubt that at a time when the world is fearful, there is a strong tendency to look for somebody to blame. And I think that given our prominence in the world financial system, it’s natural that questions are asked — some of them very legitimate — about how we have participated in global financial markets.” This was about as far as Mr Obama was willing to go, not least because in the current circumstances he is “less interested in identifying blame than fixing the problem”.

As such, he points out that the US has already taken “some very aggressive steps” to set a good example by strengthening its own regulation of financial institutions and introducing a plan to remove the toxic assets from bank balance sheets. A new regulatory framework being outlined by the G20 to ensure that the markets do not “jump the rails”, as Mr Obama put it yesterday, is also likely to include limited oversight on non-banking institutions such as hedge funds — a measure once resisted by Washington.

Mr Obama also issued a coded warning to the rest of the world that it should not take for granted America’s willingness to bear the bulk of the burden for reviving the global economy.

“The United States will do its share,” he said. “But I think that one of the things that Gordon and I spoke about is the fact that in some ways the world has become accustomed to the United States being a voracious consumer market and the engine that drives a lot of economic growth worldwide . . . In the wake of this crisis, even as we’re doing stimulus we have to take into account our own deficits.”

He is under pressure from Congress to save American jobs by raising the barriers for entering this market with protectionist measures. The message yesterday was that other countries, including those with large surpluses, such as Germany, needed to do more to promote growth.

The attention of the First Lady, however, was apparently distracted by her meeting at Buckingham Palace. “As you might imagine, Michelle has been really thinking that through,” said the President who, at the end of his press conference, appeared panicked that he had forgotten to mention the Queen.

“There’s one last thing that I should mention that I love about Great Britain, and that is the Queen. And so I’m very much looking forward to meeting her for the first time later this evening.” Given what else was on his schedule yesterday, Her Majesty would doubtless forgive being relegated to an afterthought.

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