Andy Burnham’s path to the Labour leadership has been secured, after he won the required support from trade unions linked to the party.

So far 349 of the party’s MPs have nominated the former Greater Manchester mayor, making it mathematically impossible for a rival to run against him.

Now eight of the 11 unions affiliated to Labour have said they will nominate him, paving the way for him to be crowned leader without a party vote over the summer.

Burnham is set to be unveiled as Sir Keir Starmer’s successor as Labour leader on Friday, before entering Downing Street three days later.

Although he had already cemented his status as sole candidate, party rules require him to also secure the endorsement of at least three of the 31 socialist societies and trade unions affiliated to Labour, including at least two unions.

The window during which nominations can officially be submitted will open this evening and run for 24 hours.

But in advance of the nomination period opening, a majority of Labour’s affiliated unions have confirmed they will be backing him.

The TSSA transport union confirmed it would be nominating him earlier, joining ASLEF, Community, GMB and Unison, who made announcements on Tuesday.

The Fire Brigades Union, Unite and shopworkers’ union Usdaw had all previously confirmed they would be endorsing him.

Although it raises the prospect that Burnham could secure a clean sweep of union support, Unite said its future support for his premiership would be conditional upon action for “workers and communities”.

The union said it wanted him to introduce a “wealth tax” to increase day-to-day public spending, unfreeze tax band thresholds, and loosen government borrowing rules to allow more investment in jobs and growth.

In a shot across the bows, it also called for the transition towards net zero carbon emissions to avoid “industrial vandalism”, referencing job losses in the oil sector.

As well as nominating Labour leaders, the unions play a key role in financing Labour through member contributions and one-off political donations.

The party declared £1.4m from seven different unions in the first three months of this year, around a third of its total donations during the period. It gained £4.9m in affiliation fees in 2024, according to its most recent annual accounts.