Sadiq Khan and Tessa Jowell are in a tight race as nominations close for Labour's London mayoral candidate

As Labour's London constituency parties' endorsements have rolled in, it looks like Tessa Jowell and Sadiq Khan will have a tough fight to the finish.

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Nominations for Labour's London mayoral candidate have closed, and the results reveal a close fight unfolding between Tessa Jowell and Sadiq Khan.

Under the rules, the London Constituency Labour Parties decide who they would like to nominate. Candidates must receive a nomination from at least five CLPs in order to reach the shortlist for mayor. Each CLP is allowed to nominate two candidates. For example, yesterday Hampstead & Kilburn CLP nominated both Tessa Jowell and David Lammy.

So who’s made five nominations and above?

Tessa Jowell: 63 CLPs

Sadiq Khan: 42 CLPs

David Lammy: 15 CLPs

Diane Abbott: 8 CLPs

Christian Wolmar: 6 CLPs

Gareth Thomas: 6 CLPs

The Labour mayoral contest is looking increasingly like a battle between Jowell and Khan to the top spot.

Jowell has just about remained the frontrunner for most of the contest, though she has had some significant advantages over Khan. She hasn’t had a shadow cabinet position since leaving frontbench politics in 2012, and has therefore been able to focus her attention on running for mayor – an endeavour that has long been on her radar.

Khan, in contrast, was in the post of shadow justice secretary in opposition, had a key role in running the general election campaign in London, and was also running to be reelected as MP for his semi-marginal constituency of Tooting (whereas Jowell stood down from her seat, Dulwich & West Norwood).

In spite of having less time to prepare than Jowell, Khan has made strides. Indeed, this week was the first time he became one of the bookies’ favourite for the next London mayor (William Hill put him and the Tories’ Zac Goldsmith on a joint 5/2 – to Jowell’s 11/4).

Although Jowell appears well ahead in the CLP nominations, the numbers don't tell the full story. There have, in effect, been two races going on, as the CLPs must choose at least one woman. Most seem to have given their “woman vote” to Jowell over Abbott, but Khan has been successful in the non-women-only nominations, which is a more crowded field. He has won nearly three times as many nominations as the next man on the ballot, David Lammy.

Khan has also received the backing of every trade union that has nominated a mayoral candidate, apart from Community, which has recently announced it is backing Jowell. (Affiliated supporters, such as trade unions, providing endorsements is also part of the process). It is unclear currently how much this will help Khan, as the one member one vote system means trade union members must opt in individually to vote in the primary.

But there are a lot of public sector workers in London, and insiders say the unions are aiming to register over 40,000 members to take part. This sounds ambitious, but the ballot doesn't close until 10 September (the schedule was extended after the election to match the leadership contest; initially, the ballot was due to close on 29 July).

What is clear, however, is that the race to be Labour's London mayoral candidate is tighter than it seems.

Anoosh Chakelian is senior writer at the New Statesman.