The shop workers’ union USDAW has backed Keir Starmer for Labour leader as the frontrunner opens up a commanding lead.
It means the shadow Brexit secretary is first of the candidates to make the ballot in the second round of the contest to replace Jeremy Corbyn, having secured nomination from three affiliates.
It comes after Unison, thought to be the largest UK union, and SERA, Labour’s only affiliated environment campaign, announced their support for Starmer earlier this month.
On Monday, USDAW also nominated Angela Rayner for the deputy leadership.
In a statement, the union’s general secretary Paddy Lillis said Starmer and Rayner were the right leadership team “to unite and rebuild Labour after a devastating election loss.”
“Our members desperately need Labour in power, they cannot afford another decade of Conservative governments attacking workers’ rights, incomes and public services,” he said.
“The Labour Party must be led by someone who can persuade voters that they have what it takes to be a prime minister and we are a government in waiting.”
Starmer – who is the MP for Holborn and St Pancras – said he was “honoured” by the endorsement, adding that if he was elected leader “Labour will stand shoulder to shoulder with the trade union movement”.
Starmer is increasingly seen as the candidate who can beat shadow business secretary Rebecca Long-Bailey, the favourite of the left of the party and a close of ally of Jeremy Corbyn’s.
The others in the race are shadow foreign secretary Emily Thornberry, Wigan’s Lisa Nandy – who has centred her focus on reviving Labour’s hopes in towns – and moderate Jess Phillips.
Under Labour’s new leadership rules, candidates must secure 5% (33) of Labour’s CLPs (constituency Labour parties) or three affiliates by February 14 to progress to a ballot of members.
Though many other unions have yet to announce, Unite and the Communication Workers’ Union are expected to back Long-Bailey.
Nandy, meanwhile, has won the backing of the National Union of Mineworkers (NUM) and could get support from the GMB union, whose executive meets Tuesday.
Thornberry and Phillips are trying to mobilise support among Labour’s pro-EU grassroots.
It comes amid criticism of membership hustings, with some candidates complaining that rules are too restrictive. Candidates have just 40 seconds to answer and are denied the opportunity of making an opening statement.
New figures show that more than 100,000 new members have joined the party to vote in the leadership since Boris Johnson won an 80-seat majority in December’s general election.
The winner is decided on a ballot of members by a proportional representation system known as AV (alternative vote), which sees candidates ranked in order of preference.
If one of the five wins more than 50% of first preference votes, they are declared the winner outright. However, if no candidate hits 50%, the candidate with the least support is eliminated and their second preferences are allocated to the remaining contenders. That process is repeated until one candidate reaches that crucial 50% mark.
The winner is announced at a special conference on April 4.