TLDR: young members and those who have signed up to Labour after the general election
It's no secret that Labour is undergoing some turmoil as it searches for a new leader.
A YouGov poll this week estimated that Corbyn has secured nearly half the support of those eligible to vote in a leadership contest.
The results found Jeremy Corbyn's lead is strongest with the young, with him receiving 45 per cent of his support from 18-39 year olds.
New Labour party members are also more likely to support Jeremy.
In addition, a majority of those who voted for Ed Miliband now support Corbyn - but he has the least support among those who voted for David Miliband in 2010.
So what does it all mean? In an analysis YouGov president Peter Kellner suggests that Labour's new members, affiliated trade union members and registered supporters may be swinging things somewhat. Kellner cites reports that Labour's membership had surged from 200,000 to 300,000 after the election with new registered supports and full members, saying:
On our figures, full Labour party members (including those paying the reduced student and unwaged rate) show Burnham defeating Corbyn by 50.5-49.5 per cent - a statistical dead heat; however, among those who have the vote in the current contest because they have paid a £3 registration fee or signed up as a member of an affiliated trade union, Corbyn is well ahead, with 57 per cent of first preferences and a 69-31 per cent lead in the final round.
In short, those supporters are helping Corbyn’s chances and should he win the overall contest narrowly, these voters will have tipped the balance.