The reply was polite but firm: Barack Obama regretted that he would be unable to meet David Cameron on this occasion.

When Mr Cameron visited Washington in November for a meeting with President Bush, the first such audience for a Conservative leader in five years, aides had tried to arrange a photo-opportunity with the Democrat politician who embodies youth and change.

In the event Mr Cameron left empty-handed, with aides muttering about a “logistics” problem. But that did not stop the Tory leader enthusing this week over Mr Obama’s triumph in the Iowa caucuses. “I’m enjoying watching him,” he said, “I must say I think he’s compelling.”

Over in Downing Street, Gordon Brown is privately contemptuous of what he regards as his rival’s promiscuity in his praise for US politicians and is determined not to be associated too closely with any camp.

He may even have had cause for quiet satisfaction when, just hours after Mr Cameron gushed about the rise of Mr Obama, Hillary Clinton staged an unexpected comeback in Tuesday’s New Hampshire primary.

But the Prime Minister is a keen student of US politics and knows all too well how its waves have often rippled across the Atlantic before. In a recent interview with The Times he even took to quoting Mr Obama. On Monday night he called together the group of mostly young MPs given the task of preparing Labour’s next election manifesto. Urging them not to be outflanked by Mr Cameron, he said: “Just look at the lesson of the US primaries. It’s about who owns the future.”

There is still a strong link between Mrs Clinton and the Government. This dates back to her husband’s presidency when Bill Clinton’s new Democrats provided the template for new Labour’s journey towards the political centre and the two parties regularly convened “Third Way” conferences of international thinkers.

Longstanding Clinton confidants such as Sidney Blumenthal maintain close contacts with Cabinet ministers including David Miliband and Douglas Alexander and Peter Hain. At the same time, the British political consultant Steve Morgan, who ran Mr Hain’s deputy leadership campaign briefly, is working on the Clinton team.

There are similarities in style between Mr Brown and Mrs Clinton; both emphasise experience over charisma. But Mr Brown has decided not to send any of his own staff even to observe the primaries. His allies say that he does not need to ingratiate himself with a family he has known for so long and that he “is canny enough” not to close down options with other contenders.

Channels of communication to the Clinton camp are no longer as open as they were when Tony Blair was Prime Minister. Mr Brown’s decision to employ Bob Shrum, for instance, will have been noted by the Clintons who make little secret of their disdain for the veteran Democratic consultant.

The point man for Mr Obama in London is David Lammy, the Tottenham MP, whose chance encounter with the presidential candidate might yet turn out to be his most valuable political asset. Both politicians attended Harvard Law School, and they met at a 2005 alumni party. A friend of Mr Lammy said that “as black politicians from developed countries it was inevitable that they would develop a bond”.

The British junior minister is keen not to exaggerate his links with Mr Obama, saying that they have met just three times. “They phone each other up when they want something – it’s a professional friendship,” said a source close to him.

When Mr Obama toyed with the idea last summer of arranging a grand tour of European capitals – including London, Berlin and Paris – it was Mr Lammy he called on to make the approach to Downing Street.

British officials are known to harbour mild concerns about the “untested” foreign policy stance of Mr Obama in comparison with Mrs Clinton. But there is greater alarm about an apparent lurch towards protectionism across the Democratic field – even though some diplomats believe this has more to do with electioneering than with a policy that would be implemented in the White House.

Mrs Clinton, whose husband pushed the Nafta trade deal through Congress, recently used an interview with the Financial Times to question the appropriateness of free trade and the need to conclude, at all costs, the Doha Round.

Peter Mandelson, the European Trade Commissioner, was – for once – reflecting concerns shared by Mr Brown when he responded that her comments were “misplaced” and “a disappointing sign of the times”.

On the Tory side, the energy and excitement being generated by the Democratic race may even put fresh strains on relations between British Tories and US Republicans, which have traditionally been sister parties.

Esther McVey, the party’s candidate for Wirral West, can claim to have met the black Democratic presidential candidate. A cheerleader for the new “Obamacons”, she has written breathlessly of a lunch with the senator last May and has posted a picture of them together on her blog.

George Osborne, the Shadow Chancellor, has dispatched two junior aides, Rupert Harrison and Rohan Silva, to monitor the US primaries. One was said to be “bursting out of his skin with excitement” after attending an Obama event.

When Mr Cameron visited the White House on November 30, it was to heal a five-year rift that had been opened up by his predecessor, Michael Howard, who infuriated Mr Bush by making “opportunistic” criticism of Tony Blair’s unflinching support for the Iraq war. Mr Cameron made matters worse by using the anniversary in 2006 of the September 11 attacks to criticise Washington’s neoconservative foreign policy. It may have been significant that when Mr Cameron was asked at a Washington press conference what he could learn from US Republicans, he preferred to keep his distance. The two countries had “very different political systems”, he explained.

The prominence of socially conservative presidential candidates such as Mike Huckabee and Mitt Romney in the Republican race jars with the liberalism of Cameroonian Conservatives.

Mr Cameron’s team is divided in its loyalties. The likes of the MPs Boris Johnson and Simon Burns are backing Mrs Clinton. Liam Fox, the Shadow Defence Secretary, is known to be holding out for the Republican Rudy Giuliani. The Tory leader has good links to both John McCain and the Mayor of New York, Michael Bloomberg, who is said to be considering an independent run for the White House.

As for his attempt to have Mr Obama shed some stardust over him, the Tory leader should not be too disappointed. The Democratic presidential candidate has also spurned invitations from other visiting opposition leaders for meetings.

For all his talk of changing America’s face to the world and rebuilding old alliances, Mr Obama has been notably reluctant to engage, particularly with Europe. As British and European leaders ponder the meaning and consequences of Mr Obama’s sudden rise, perhaps they should be asking instead how much they really matter to him.

Friends and foes

— Ronald Reagan and Margaret Thatcher mutually reinforced the conservative revolution of the 1980s, with the President going out of his way to humiliate a visiting Neil Kinnock in 1987

— John Major was caught out when accusations of British dirt-digging on Bill Clinton soured his relations with the subsequent victor of the 1992 presidential election

— Tony Blair and Gordon Brown were among those to benefit, with a US-inspired new Labour. Mr Blair repaid the favour with unstinting backing for Mr Clinton throughout his travails over the Lewinsky affair

— Ties between the Democrats and Labour were strained by Mr Blair’s support for President Bush over Iraq . . .

— As were those between the Republicans and the Tories. Michael Howard was snubbed by the Bush presidency, and David Cameron’s meeting with Mr Bush was limited to 15 minutes

How they poll Republican voters
McCain 22%
Huckabee 20%
Romney 20%
Giuliani 9%

Democrat voters
Clinton 35%
Obama 33%
Edwards 15%

Sources: Rasmussen Reports, January 11 2008

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