UK campaigners have claimed British-based Democrat voters are a "secret weapon" in the drive to keep Donald Trump away from the White House.
Democrats Abroad UK (DAUK) is stressing it is not too late for Americans to register to vote, less than a week until the election.
DAUK said it estimates there are more than 200,000 Americans currently living in the UK who are eligible to vote by absentee ballot.
The group is calling on US citizens based in Britain to make sure "every vote counts" in the race to the Oval Office.
DAUK chairman Robert Ravelli said: "We want to make sure we get every single vote we can possibly get in the UK.
"We will be spending a lot of time between now and Tuesday to do so."
Deputy chairman of DAUK Inge Kjemtrup said more Americans want to have their say in the election.
She told the Press Association: "Donald Trump has been our best recruiting agent.
"I think this election has been a huge motivator for people."