A respected Labour lobbyist and party insider has said that Jeremy Corbyn is on track to be only narrowly beaten to the Labour leadership.

Luke Akehurst predicted that Corbyn would “only lose on final transfers”.

On Twitter, he went on to suggest that Labour’s vote share would drop to 15 per cent if Corbyn did manage to win the contest.

Akehurst, who is backing Yvette Cooper, is a leading figure and campaign mastermind in the Hackney North constituency Labour party.

He sat on the party’s National Executive Committee from 2010 to 2012 and has many years’ experience as a lobbyist at the London HQ of global consultancy Weber Shandwick.

The call comes after the Unite union's executive committee voted on Sunday to lend its support to Corbyn, with Burnham as its second preference.

The union is Labour’s most generous donor and its decision is a major boost for the left winger’s campaign. However, the unions are expected to have less influence on this year’s contest now that Labour has moved to a one member, one vote system for choosing its leader.

A spokesman for the union said:

“The backing for Jeremy Corbyn was in recognition that his policies were most closely aligned with those of Unite.”

The union will not back any of the candidates for deputy leader, but will recommend that its members support either Angela Eagle and Tom Watson.