Barack Obama is mounting an unprecedented push for the votes of tens of thousands of UK-based Americans, who his campaign believes could have a decisive impact on the US presidential election.
The Democratic Party has been quietly deploying the full machinery of electioneering here, ranging from telephone canvassing to on-the-street campaigning by volunteers around the UK.
Dozens of wealthy expat Americans are paying $10,000 (£5,500) a head to attend an Obama fundraising lunch in Whitehall today. Among those breaking bread will be actresses Gwyneth Paltrow and Kate Hudson, the former US presidential candidate Al Gore, the River Cafe chef Ruth Rogers and Joshua Berger, president of Warner Brothers UK. Rogers will hold a more intimate dinner at her home later tonight, where diners have been asked for "suggested contributions" of $2,500 (£1,350).
An estimated 250,000 to 300,000 US citizens are resident in the UK, representing a sizeable chunk of the six million Americans living overseas. They are entitled to vote by post in their home states.
And after just 537 votes in Florida handed victory to George Bush in the 2000 presidential contest, Obama's campaign is pulling out the stops to maximise the UK-based Democratic vote, with the prospect that the 4 November presidential poll could similarly produce another photo-finish.
A growing volunteer army of Democrats are handing out leaflets in towns and cities including Edinburgh, Brighton, Leeds, Cambridge and Oxford. In London, teams of volunteers are seeking out Americans in busy shopping areas such as Oxford Street and High Street Kensington.
In addition, a substantial though unknown amount of money has been raised in the UK for Obama's campaign.
Standing under a clutch of red and blue balloons amid the crowds at London's Borough Market, Jill Adams said she was campaigning for the first time. "I have never been politically active before, but I have become so worried that if John McCain and Sarah Palin are elected then we could be facing World War Three.
"I am terrified of their foreign policy," said the 52-year-old New Yorker who came to live in Britain 11 years ago with her English husband. Elsewhere, volunteers have been working in shifts through the week in a phone-bank operation to contact as many potential supporters as possible.
The UK campaign for Obama's Republican rival John McCain has been lower profile, though no less dedicated. "The Democrats have a significantly higher membership than us because they don't charge for membership and our structure is different – we are legally separated from the Republican Party," said Miki Bowman, UK country chair for Republicans Abroad.
McCain supporters say that while the Obama campaign can count on the votes of a large proportion of US students studying in Britain, US service personnel at overseas military bases are a natural constituency for the Republican presidential nominee, himself a war veteran.
votes handed victory in Florida to George Bush in the 2000 election.
Americans living in the UK.