Jeremy Corbyn is "cautious" about his chances of victory in the Labour leadership contest despite an opinion poll giving him a clear lead and the bookmakers installing him as favourite to win.
The veteran campaigner said he found the "Corbynmania" which has seen thousands of people pack into venues to hear him speak "a bit embarrassing".
The left-winger now has the support of more than half of those with a vote in the Labour leadership contest, a YouGov poll suggested.
The survey for The Times of 1,411 eligible voters in the contest to succeed Ed Miliband found Mr Corbyn had nearly doubled his lead in a week to 32%.
It gave him 53% - enough to win without a need to count second preferences - with Andy Burnham losing five points to 21%, Yvette Cooper slipping two to 18% and Liz Kendall down three on 8%.
Mr Corbyn said: "The campaign is going very well but I think we should be a little bit cautious because there is still time for people to register to join the party or register as supporters and no ballot papers have yet been sent out and we won't know the result until next month. So let's be a bit cautious."
The Corbyn campaign has continued to gather momentum despite warnings from a string of senior party figures that choosing the veteran left-winger would be catastrophic for Labour's electoral chances, with one grandee comparing him to former Tory leader Iain Duncan Smith.
Islington North MP Mr Corbyn told BBC London the contest was "very democratic", with large numbers of people taking part including some who had not been involved in party politics before.
"If they choose somebody as leader that the others don't like, well, I think they have to accept there's a democratic process," he said.
Mr Corbyn said he wanted a "set of aims and values for the party" that "was prepared for public ownership or public administration of key industries" such as Royal Mail and the railways but denied this was an attempt to reinstate Clause IV of the party's constitution.
"It is not going to be the same wording that I am going to suggest as the old Clause IV, that was written in 1918, I think we need something that reflects modern society," he said.
Tony Blair's former spin doctor Alastair Campbell has urged Labour supporters to sign up to vote for "anyone but Corbyn" to help the party "stop itself driving over a cliff".
Lord Soley, a former chairman of the Parliamentary Labour Party, compared the prospect of a victory for Mr Corbyn to Mr Duncan Smith's disastrous leadership of the Conservatives.
Serial rebel Mr Corbyn had been accepted as a "maverick" within the party but discipline was needed in Parliament, Lord Soley said.
He added: "It might focus minds before this important vote if we recall how delighted we were when Iain Duncan Smith became leader of the Tory party. We wanted him to stay. We should not fall into the same careless way of thinking."
Bookmakers have slashed the odds on a Corbyn victory following the YouGov poll.
William Hill cut Mr Corbyn's odds twice in just two hours as money piled in for the left-winger following the survey, with bets of up to £2,000 recorded.
At 9am he was a 5/4 shot, yet by 10am he had been trimmed to 1/2 and less than an hour later he was as short as 1/3.
Spokesman Graham Sharpe said: "We can recall no other example of a 200/1 chance becoming an odds-on favourite in a political betting market in our 50-plus year history of political betting."
Ladbrokes said Mr Corbyn was the "red-hot favourite" after his odds collapsed in recent weeks.