Labour's London Mayoral candidate to be announced amid close-run result between Tessa Jowell and Sadiq Khan

Dame Tessa, a former Cabinet minister, has been the favourite throughout the contest

A close-run result is expected between Dame Tessa Jowell and Sadiq Khan in the contest to find Labour's candidate for Mayor of London (Getty)

Labour’s candidate for Mayor of London is set to be announced, with a close-run result expected between Dame Tessa Jowell and Sadiq Khan.

Dame Tessa, a former Cabinet minister, has been the favourite throughout the contest to secure the nomination and attempt to win political control of the capital back from the Conservatives next May.

But early calculations were thrown into doubt by the surge of support for Jeremy Corbyn in the leadership contest and the uncertainty over its impact on the shape of the party in London.

More than 110,000 Londoners were entitled to take part in the election compared with 41,000 Labour members four months ago.

The assumption is that many of the new members, supporters and trade union affiliates are on the left and could baulk at Dame Tessa’s reputation as a loyal Blairite.

However, she has the highest public profile of the six candidates and the cachet of her role in bringing the Olympic Games to London three years ago. Polls have also suggested she would be best placed to defeat the likely Tory contender, Zac Goldsmith.

However, Mr Khan, the former shadow Justice Secretary, has run a spirited campaign and is expected to pick up second and third preference votes from other candidates, while his decision to nominate Mr Corbyn for the leadership could attract left-leaning activists.

The performance of the veteran MP Diane Abbott, a close ally of Mr Corbyn, will provide a useful gauge of whether the party has shifted to the left in London.

The former minister David Lammy has won plaudits for his campaign in a contest which has largely lacked the rancour which has soured the leadership battle.

The other two candidates, the Harrow MP Gareth Thomas and the transport campaigner Christian Wolmar, are also expected to score respectable results.

A source in Dame Tessa’s team said: “Our numbers look good, but you can never be sure in a process like this.”

The winner will be elected under the same system for choosing the Labour leader. The candidates with the fewest votes will drop out in succession with their supporters’ second preference votes redistributed until someone acquires 50 per cent support.