JEREMY CORBYN supporters are “confident” of securing a historic victory for the left in Labour’s leadership contest today — despite a low trade union turnout.

After a grueling 119-day campaign which saw Mr Corbyn address more than 55,000 people, the new party leader will be revealed in London at lunchtime.

Sources close to the left candidate said his prospects look “very, very promising” after union-backed Sadiq Khan won Labour’s London mayoral selection yesterday.

Mr Khan won handily yesterday despite reports that turnout among union members could be just a fifth of the number that voted in the 2010 leadership election.

Around 50,000 affiliated supporters are believed to have voted — down from 211,000 when Ed Miliband was elected.

And fewer than 10,000 trade union sign-ups voted in the party’s London mayoral selection process.

Yet Mr Khan, supported by the GMB and Unite unions, defied expectations to beat Blairite Tessa Jowell, polling 48,152 compared to her 33,573.

He was 11,000 votes ahead in the first round of voting and, after transfers from other candidates, extended that to 14,000.

Unite London and south east secretary Peter Kavanagh said the result was a “vindication of the progressive polices he set out during the campaign.

“On housing, transport and employment Sadiq offered a positive vision that will deliver the change Londoners are crying out for,” he said.

The result was widely viewed as a win for the left of the party and a boost to Mr Corbyn’s chances of storming to victory today.

A Campaign for Labour Party Democracy spokesman told the Star: “I was confident before that result, but I’m very much more so now.

“I expected Tessa to win — she had a very well run and very well funded campaign.

“Jeremy will do extremely well among registered and affiliated supporters, but this shows it certainly won’t rest on those voters.

“He could win among every section.”

Having started as a 100/1 outsider, Mr Corbyn finished the contest as the 1/20 favourite.

Ladbrokes was among bookies who cut the odds on the left candidate becoming leader again last night as a result of Mr Khan’s victory.

“Corbyn was already likely to win, but the mayoral results confirm that,” said Ladbrokes head of political betting Matthew Shaddick.

“He is probably going to win and win quite easily too.”

Yvette Cooper looks poised to come second in the first round and will hope to secure victory with transfers from beaten rivals Andy Burnham and Liz Kendall.

But Ladbrokes made Mr Corbyn evens to win in the first round by claiming between 50 to 60 per cent of first preferences.

An eve-of-declaration online poll by Labour List gave Mr Corbyn 52 per cent of first preference votes, with Ms Cooper on just 23 per cent.

Andy Burnham was set to come third with 13 per cent and Liz Kendall last with 12 per cent.