Battle heats up for UK's expat votes

James Cusic joins Democrat volunteers campaigning to mobilise Britain's 250,000 eligible American voters

For John McCain's 2008 London fundraiser it was the plush Spencer House in St James, once the home of Princess Diana's ancestors. Four years on from Mr McCain's defeat, the Republicans' latest attempt to recapture the White House has London's über-wealthy American bankers, fund managers and lawyers heading for Mayfair and a Grade 1 Georgian mansion where the presidential hopeful Mitt Romney will hold a $75,000-a-plate fundraising dinner next week on the eve of the Olympics.

With Barack Obama warning that a sitting president will be outspent in a campaign by his opponent for the first time in history, London's expat Democrats have reacted to their party's call-to-arms by shunning Mayfair, at least for the moment, and instead concentrating on the grassroots.

While the Romney bash is now looking to fill the expensive empty chair of Bob Diamond, who pulled out from the high-end fundraiser last week, the Democrats were heading for The Ritz – not to the hotel, but the Blue Posts pub round the corner. With the Mayfair locus for Mr Romney's City supporters likely to look straight out of a Condé Nast centre-spread, the fish and chips platter upstairs at the Blue Post looked more miners gala than West Wing glamour.

For Michael Lange, a management consultant who has lived in London for 22 years, the gathering ended a Sunday of walking on Oxford St and High Street Kensington carrying a Stars and Stripes and handing out leaflets reminding his fellow American citizens in London that their vote still counts. "We found an elderly couple in their 60s from West Virginia who didn't realise they were entitled to a postal vote," he said, sounding like he'd just struck electoral gold in Chelsea.

Lange's effort is part of a Democrats Abroad summer offensive that has already involved a five-week, 27-city, 13-country, European tour.

Around a quarter of a million Americans based in the UK can vote in November's election. It is estimated that 70 per cent lean towards the Democrats.

The "Romney – Believe in America" campaign has hired the upmarket fundraiser ScottPrenn to help focus on those capable of writing big cheques for next week's European fundraiser. And the firm, i has learned, is being unofficially assisted by senior UK Conservative aides helping them connect to London's Republican rich.

Tory headquarters says it doesn't have a problem with party aides being part of the Romney machine this side of the Atlantic but they were less forthcoming about confirming whether Conservative ministers or MPs are meeting the Republican candidate on his Olympic visit.

If Mr Romney loses and Mr Obama remains in the White House for a second term, covert Tory campaigning for Mr Romney will do little for the Cameron-Obama special relationship.

A spokesman told i: "The Republicans are our sister party. We are all part of the international alliance [of centre and centre-right parties] led by John Howard, the former Australian prime minister. And I'm sure Ed Miliband will be holding a fund-raiser for Obama."

It is illegal under US Federal Commission laws for any British citizen to donate money to an American presidential campaign. Those paying to attend and write cheques for Mr Romney in London this month will all need to be US citizens and may be asked to bring passports.

Republican insiders predict Mr Romney will head home from London with more than $2m to help his campaign. The cash is likely to have come from a tight, connected group: employees of Goldman Sachs, HSBC, magic circle attorneys, private equity gurus and super-rich Americans who simply prefer London to New York.

These Republicans will be unlikely to grace the Blue Posts pub. Inside the Ritz itself is a better bet.