A new cross-party campaign for Britain to exit the European Union is the clear front runner to be designated the official "out" campaign in the forthcoming referendum, a leading supporter has said.
The Vote Leave campaign has launched with the backing of some of the biggest political donors in the country as well as prominent figures from the world of business and MPs across the political spectrum.
It now faces a battle with the rival umbrella group, Leave EU, launched by wealthy Ukip backer Arron Banks, to win the designation of the Electoral Commission as the official "out" voice in the referendum on Britain's EU membership.
Whichever group comes out on top will enjoy significant advantages including higher spending limits, campaign broadcasts, free mail shots and public funding of up to £600,000.
But while Ukip's leader Nigel Farage has pledged to work "hand in hand" with Leave EU, the party's only MP, Douglas Carswell, has come out firmly for Vote Leave.
"It would be bad for Ukip and it would be bad for the 'out' campaign if we were to cut ourselves off from the campaign I believe most likely to get the designation," he told Sky News.
"If we'd been having this conversation a month ago I would have said it would be a two horse race. I now suspect it's a one horse race. We really don't want to cut ourselves off from a very effective campaign."
The two men have already clashed on the issue, with the Ukip leader accusing Mr Carswell of "residual loyalties" towards the Conservatives he used to represent before defecting to Ukip.
The eurosceptic Conservatives for Britain are among the groups supporting Vote Leave.
Mr Carswell had a furious row with Mr Banks at the party's annual conference last month in Doncaster, claiming he been threatened with de-selection as a Ukip MP if he did not fall in line behind Leave EU.
It sets the stage for a potentially bitter and divisive struggle between the two groups as they head towards the referendum which must be held before the end of 2017.
In a statement, Leave EU co-chairman Richard Tice welcomed the fact that Business for Britain - another of the groups behind Vote Leave which had previously campaigned for "fundamental changes" in the UK relationship with the EU - was now in favour of leaving altogether.
"We look forward to supporting their push to persuade business across the UK to support an EU exit," he said.
However Mr Carswell was dismissive of Leave EU, suggesting it lacked the campaigning experience which Vote Leave enjoyed, including Matthew Elliott, the founder of the Taxpayers' Alliance, and Dominic Cummings, a former special adviser to Michael Gove.
"Getting a whole bunch of likes on Facebook is not the same as winning a referendum," he said.
Vote Leave's co-treasurers number some of the wealthiest political donors in the UK - ex-Tory treasurer and banker Peter Cruddas, Labour donor and mail-order millionaire John Mills and spread betting tycoon Stuart Wheeler, who was a major donor to the Conservatives before becoming Ukip treasurer.
It has also signed up MPs from the Conservatives, Labour and Ukip, including Tory ex-Cabinet minister Owen Paterson, and the Labour Leave group.
Other prominent supporters include another ex-Tory treasurer, the former Dixons chairman Lord Kalms, former Channel 4 chairman Luke Johnson, author Frederick Forsyth, Green Party peer Baroness (Jenny) Jones, historian Andrew Roberts and Nobel Peace Prize winner Lord Trimble.