The education secretary had the backing of 44 colleagues as of 6pm on Tuesday, according to the first official tally released by the Parliamentary Labour Party (PLP) since nominations opened.
Former Commons leader Lucy Powell, who was sacked by Sir Keir Starmer in his reshuffle last week, is close behind with 35, followed by backbenchers Bell Ribeiro-Addy with eight, Dame Emily Thornberry with seven and Paula Barker with three.
Housing minister Alison McGovern is currently coming last with two nominations, though sources on her campaign team suggested this did not reflect the true level of support behind her.
Candidates have until 5pm on Thursday to receive the backing of 80 colleagues, meaning there is still plenty left to play for as less than 100 MPs have made their official nominations so far, out of 398.
A fresh tally will be published by the PLP on Wednesday evening, though MPs may publicly reveal who they are backing before then.
Those not on the PLP’s current list include Southport MP Patrick Hurley, who has thrown his weight behind Ms McGovern in a post on X.
Candidates will have the chance to woo undecided colleagues during a hustings event on Wednesday evening, but there are fears it could descend into chaos as the event will be held online only.
That means hundreds of MPs will have just one hour to quiz the six contenders virtually. It is not clear if or how the event will be moderated.
Ms Barker, the MP for Liverpool Wavertree, expressed concern about the logistics of the contest.
Asked if she feels confident she can get the numbers, she told Sky News: “I think the very tight timeframe and the fact hustings for MPs are being held online 8pm – 9pm when the majority of colleagues are travelling home undoubtedly compounds the issue.
“Of course, that is an issue to be addressed by whoever wins the race and at this moment in time we are all in the same boat.”
However, a Labour source defended the decision, saying: “There’s frankly no convenient time to do it. Ministers will have busy diaries serving the public during the day… priority has to remain public service.”
Ms Ribeiro-Addy has also criticised the contest’s rules, telling Sky News’ Politics Hub with Sophy Ridge that having just a few days to get 80 nominations “doesn’t feel right”, especially given the winner is “ultimately decided by members”.
Candidates who make it through the first round must go on to win the support of either 5% of Constituency Labour Parties (CLPs) or three organisations affiliated to the party, two of which must be trade unions.
The successful candidates will then appear on the ballot for a vote of all party members and affiliated party supporters, with results declared on 25 October.
The six-week timeline was set by Labour’s ruling National Executive Committee but will be overseen by the party machinery who insist they will work with all candidates to give them a fair hearing.
There are many MPs and ministers who want to see the contest done quickly, to avoid it being a distraction from the government’s priorities.
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The race was triggered by the resignation of former deputy prime minister and housing secretary Angela Rayner after she admitted underpaying stamp duty on a flat she bought in Hove.
Following calls for her replacement to be a Northern woman, all six candidates who entered are female, though Ms Ribeiro-Addy and Dame Emily represent seats in London.
Ms Phillipson and Ms McGovern are seen as candidates that would remain loyal to Number 10, which some MPs want to see to avoid the party becoming more divided. They both honed in on their Northern roots while pitching themselves as the candidate to take on Reform UK when announcing their deputy leadership bids on Tuesday.
Clapham and Brixton Hill MP Ms Ribeiro-Addy is seen as the left-wing candidate, and has the backing of many MPs in the Socialist Campaign Group (SCG) such as Corbynite Richard Burgon.
However, Ms Baker, a former trade union official and Ms Thornberry, chair of the foreign affairs committee, have also vowed to challenge the government on issues like welfare and Gaza.
Manchester Central MP Ms Powell was recently ousted from government and said she decided to stand “after much encouragement” from colleagues.
A Survation survey of 1,308 Labour members who read the LabourList website suggested Ms Phillipson was the most popular choice for the role.
