Farage thinks Remain has carried referendum as votes are counted
Ukip leader Nigel Farage has said he believes Britain has voted to remain in the European Union, on the basis of exit polls conducted by friends in the City.
Mr Farage told the Press Association that information he has received from contacts within the finance industry chimed with his personal assessment of voting in the referendum.
His comments came as counting of millions of votes continued in what could be the largest democratic exercise ever conducted in the UK.
Conservative supporters of Brexit including Boris Johnson and Michael Gove wrote to David Cameron urging him to stay on as Prime Minister regardless of the result, as Tories battled to restore a unity riven by weeks of divisive "blue-on-blue" fighting.
With no exit polls conducted by broadcasters, a reliable picture of the likely outcome was not expected to emerge until the early hours of Friday, with the final result expected at breakfast time.
Mr Farage told the Press Association: "I don't know but I think Remain will edge it, yes. The massive increase in voter registration will be the reason for that."
Asked if he was just experiencing election night jitters, the Ukip leader replied: "It is a calm and rational feeling. If I am wrong, I would be thrilled. But it is what we have seen out and about and what I know from some of my friends in the financial markets who have done some big polling."
Some 84 Tories signed the letter which was handed to 10 Downing Street as polls closed at 10pm. They told Mr Cameron: "We believe whatever the British people decide you have both a mandate and a duty to continue leading the nation implementing our policies."
As well as Mr Johnson and Mr Gove, the signatories included Cabinet-level Brexit backers Chris Grayling, Theresa Villiers and John Whittingdale.
But former Cabinet ministers Owen Paterson, Cheryl Gillan and David Jones did not sign, along with influential backbenchers David Davis and Bernard Jenkin.
Former work and pensions secretary Iain Duncan Smith, who quit the cabinet weeks before the referendum, did not sign but said he thought Mr Cameron should stay on.
Tory MP Robert Syms said that two-thirds of Conservative MPs who broke with the PM to back Leave had signed the letter, but said it had not been possible to reach all of them to ask them to sign.
Labour's Jonathan Ashworth said that the letter could not "unsay" the comments of Tory MPs who have spent the last few weeks attacking the PM.
"This letter exposes the reality that David Cameron and the Conservative Party are now utterly preoccupied with leadership infighting rather than the future of the country," said Mr Ashworth.
"What's more this letter cannot unsay what senior Tory politicians have been telling us for weeks - that the British people simply cannot trust David Cameron."
Sterling rose 1% against the US dollar in overnight markets amid speculation that Remain has won the referendum.
But Mr Grayling refused to follow Mr Farage in predicting the result.
And Leave.EU said that it had conducted an "internal poll" of 10,000 people which suggested that Brexit was leading by 52% to 48%.
"I think we're only going to know the full picture as the night goes on," said Mr Grayling."I think perhaps I'll wait and see what actually happens when the votes are counted."
Environment Secretary Liz Truss said she was "optimistic" about a positive result for Remain while Education Secretary Nicky Morgan said she was "confident and hopeful" of victory for the In camp.
And pro-Brexit Northern Ireland Secretary Ms Villiers told Sky News: "My instinct is that Remain has won ... I suppose I would put it down to Project Fear succeeding."
However, she said it was "crucial" whatever the vote that David Cameron stays on as Prime Minister because the UK will need "political stability".
Mr Grayling said it would be an "absolute nonsense" for Mr Cameron to lose his job given that he won an election just over a year ago promising to hold a referendum.
"It would be an absolute nonsense if David Cameron felt, having given the country that choice, if they take the decision he couldn't carry on the job," he told Sky News.
"We are completely behind him staying, we want him to stay and that letter is a statement of commitment to his leadership."
A high turnout was expected in the referendum, despite torrential rain in South-East England which forced the closure of some polling stations and caused transport disruption for commuters planning to vote on their way home.
A record 46,499,537 voters were eligible to take part, said the Electoral Commission, meaning that a turnout a little over 72% could surpass the highest number of votes ever in a general election.
Gibraltar, which is taking part in the referendum as a British overseas territory within the EU, was the first area to declare with an overwhelming victory for Remain by 19,322 to 823 on a healthy turnout of 84%.