Jeremy Corbyn: It's going extremely well

Jeremy Corbyn says his leadership campaign is going "extremely well" but that talk of him winning the contest is "a bit premature".

The left-winger is ahead of his rivals in the race to replace Ed Miliband, according to a Times opinion poll.

He also dismissed claims that he would split the party if chosen as leader.

The Islington North MP was speaking to journalists after promising a "publicly led expansion and reconstruction of the economy" in a speech in London.

His comments came after former prime minister Tony Blair said he would take the country backwards if elected and that anyone with his politics in their heart should "get a transplant".

'Rather silly'

"I do not know what he means by taking the country backwards," Mr Corbyn said, adding that Mr Blair's suggestion he was the Tory preference amounted to "rather silly remarks".

"Surely we should be talking about the situation facing Britain today, the situation facing many of the poorest people in this country today, and maybe think if our policies are relevant," he said.

"A lot of people are supporting us, particularly young people supporting us who want a very different Labour Party to the one they've had in the past."

In his speech on the economy, Mr Corbyn said austerity was a "political choice not an economic necessity".

Analysis by Anthony Reuben, BBC News head of statistics

You would expect people who are eligible to vote in the Labour leadership contest to be unusually interested in politics.

But the full details of the poll show that of the 1,056 people polled, 80% said they would definitely be voting in the leadership election while another 15% said they would probably be voting.

I know that the rules for the leadership election have been changed, but it still seems a very high turnout.

Compare it with the 2010 leadership election, when about 72% of constituency Labour Party members voted.

Labour poll: have we learned nothing?

He promised to protect public services and increase taxes on the wealthy, arguing that "all of us are an accident away from needing a benefits system that sustains us

The YouGov poll for The Times suggests that in the final round of voting, the Islington MP would get 53% of support, six points ahead of Andy Burnham. Liz Kendall and Yvette Cooper are also in the contest.

'Testing mettle'

Mr Corbyn only made it onto the ballot paper at the last minute after MPs who supported other candidates "lent" him their nominations to get him into the contest, arguing Labour needed as wide a debate as possible about its future direction.

John McTernan, a former adviser to Tony Blair, has described those MPs who helped him reach the leadership shortlist as "morons".

Mr Corbyn dismissed this, saying: "I don't get involved in personal stuff, it's really not worth it. That kind of remark is really uncalled for in any kind of politics."

Labour peer Lord Foulkes said those who nominated Mr Corbyn despite disagreeing with him should be "searching their consciences right now". They should "realise they've put the Labour Party in to a very difficult position", he told the BBC.

But Frank Field, who nominated Mr Corbyn despite disagreeing fundamentally with him about economic policy, said the other candidates had failed to articulate an alternative to Mr Corbyn's stance of "deficit denial".

"I would be surprised if Jeremy wanted to win. He really wanted to test the arguments and the mettle of the other candidates," he told BBC News. "He has played his role. Sadly we have not had the other candidates with the abilities to take him on and say...'this is my vision, these are my priorities, there are my values'."