More than half a million Labour members and supporters have voted to choose the next leader.

Pollsters and bookmakers think that Jeremy Corbyn – a previously obscure left-wing backbencher who is opposed to the monarchy – is about to become leader of Her Majesty’s Most Loyal Opposition.

We’ll find out at a special conference on Saturday. Is this contest a done deal? And what would a Corbyn win mean for Labour?

Who’s going to win?

Most polls carried out since the beginning of August have put Jeremy Corbyn in the lead.

A month ago, a YouGov poll for the Times put the leftwing candidate way out in front with 53 per cent of people eligibile to vote saying they would give their first preference vote to Corbyn, compared to 21 per cent for Andy Burnham, 18 per cent for Yvette Cooper and 8 per cent for Liz Kendall.

More recent Opinium polls of Labour voters also have Corbyn well out in front, although with a smaller lead.

A big note of caution is needed here, as opinion polls are not always right: most of the surveys carried out before the 2015 general election predicted the wrong result.

If no one reaches 50 per cent in the first round of voting, second preference votes are counted, which could see Andy Burnham or Yvette Cooper become leader of the opposition.

Why is Corbyn in the lead?

According to the last figures Labour put out, 553,954 people had a vote in this contest.

That includes 292,973 fully paid-up party members, 148,182 affiliated supporters – mainly union members who chose to take part – and 112,799 registered supporters who took advantage of an offer to vote in the leadership election after paying £3.

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The total “selectorate” will be slightly smaller now: Labour told Channel 4 News’s Michael Crick yesterday that they have so far weeded out 4,500 people who tried to sign up for not sharing the aims and values of the party.

This follows allegations that hard-left “entryists” as well as supporters of other parties like the Tories and the Greens had tried to infiltrate the party by paying £3 to become a registered supporter.

But the relatively low numbers of people struck off the list for infiltration suggest this may have been overblown. Many more names were removed because they had been duplicated or could not be found on the electoral register.

These membership figures suggest that the number of people eligible to vote has risen from 187,000 to just over 550,000 since the general election in May. So about two thirds of voters are new to the party.

And YouGov research suggests that people who joined after Labour’s loss in May tend to be the most strongly supportive of Corbyn.

But it’s worth noting that in its latest poll, YouGov was able to differentiate between full Labour members, affiliated supporters and registered supporters who have paid £3 to vote:

Even if you strip out everyone who registered as an affiliate supporter or a £3 registered supporter, Corbyn is still the most popular candidate.

Could there be a challenge to the result?

It’s possible that various controversies surrounding the way the contest has been held could lead to someone challenging a Corbyn victory in the courts, although there appears to be little appetite for this among the other candidates.

Concerns about “Tory infiltrators” led Burnham campaign director Michael Dugher to hint at a potential lawsuit in a letter to Labour’s general secretary last month.

But all four candidates have since played down the “entryist” story and ruled out mounting legal action.

Tottenham MP David Lammy yesterday called for an “inquiry” after saying one in five potential voters in London had not received their ballot papers.

He said: “The extent of this across the country needs proper inquiry and proper understanding and whether it has affected the ultimate vote, I do not know.”

Will Labour MPs back Corbyn?

There are already rumblings in the media of backbench rebellions against Corbyn.

Liz Kendall has already said she will not vote against her principles on issues like Britain’s membership of Nato, the renewal of the Trident nuclear deterrent or EU membership.

The Guardian reported this week that eight members of the shadow cabinet will not serve under Corbyn and five more are doubtful.

Labour backbencher Mike Gapes said: “Jeremy will not encourage the same loyalty as Ed Miliband did, because he showed none to previous leaders.”

There’s some truth in this. Corbyn’s disloyalty is a matter of public record. He has voted against the Labour whip on hundreds of occasions and was the party’s most rebellious MP between 1997 and 2010, according to academics Philip Cowley and Mark Stuart.

Can Labour win with a left-wing leader in charge?

The argument over whether Labour lost the last election because it was too left-wing continues to rage.

Some, including Unite leader Len McCluskey, say this is a myth. Labour lost because it did not come out strongly enough against austerity, or so the argument goes.

Mr Mcluskey said: “Millions of people voted for parties perceived as to Labour’s left – the SNP and the Greens. Even more voted for Ukip and in many cases they too were expressing hostility to elite economics.”

But research commissioned by Labour MP Jon Cruddas last month suggested that a harder anti-austerity stance would not have been a vote-winner.

It found that 58 per of voters agreed that cutting the deficit was the “top priority” for the government, while only 16 per cent disagreed.

Adam Ludlow from pollsters ComRes says polling shows that “the vast majority of voters thought that Labour and the Conservatives were different in their visions for the future of the country, their attitude to the economy and their attitude towards government spending”.

“Contrary to what some might say, the public did not think that the choice on offer was just different shades of austerity. Labour did not lose because they didn’t offer a big enough alternative to the Conservatives on the big issues.”

Peter Kellner from YouGov notes says voters’ attitudes don’t fit neatly into “left” and “right” categories.

Many people support the idea that the government should punish companies who dodge taxes and exploit their workers – an idea central to Ed Miliband’s campaign. But the same people agreed with the Conservative policy that tax cuts should be prioritised over increases in benefits.

The answer, according to Kellner, is that voters have a “passion for fairness” that cuts across the old divisions of left and right.

He points out though, that parties perceived as significantly left or right of the centre ground tend to do badly at elections – as evidenced by the failure of Neil Kinnock, William Hague, Michael Howard and Ed Miliband.