Len McCluskey is poised to make an audacious bid to remain as the head of Britain’s biggest union, to shore up support for Jeremy Corbyn.

The Unite general secretary has told members of the union that he plans to quit and force an early election – with the intention of winning again and staying in charge until 2020.

The resignation could come as early as tomorrow, with the fresh election for general secretary to take place next year.

At present, Mr McCluskey, 66, is expected to retire when his current five-year term ends in 2018.

His departure would be welcomed by anti-Corbyn Labour MPs who see his vocal and financial support for Mr Corbyn as vital in strengthening the Labour leader’s position.

But his supporters want him to extend his leadership of the union up to the next general election, which is expected in 2020.

Unite supporters hold crucial votes on Labour’s national executive committee and Mr McCluskey’s friend, Karie Murphy, is Mr Corbyn’s office manager.

The union’s rules state that elections can only take place before the end of the general secretary’s five-year term if he or she retires, resigns or dies.

Last week, it was claimed that the general secretary hoped to overturn the rule by getting support from three-quarters of the union’s executive committee.

But it is now believed that Mr McCluskey has decided not to seek to change the rules after realising that he would struggle to gather enough support.

Instead, he will stand down within days to spark an early election next year, a meeting of the Unite executive committee is expected to be told today.

Unite is Britain’s biggest union, with 1.4 million members, and provided Mr Corbyn’s 2015 campaign for leadership with £175,000 as well as office space.

Mr McCluskey, born in Liverpool, is a former Militant sympathiser who served as the national secretary of the TGWU general workers group from 1990.

In 2007, he was appointed as the assistant general secretary of the newly created Unite which was founded through a merger of the TGWU and Amicus.

He was elected as general secretary in November 2010 and played a decisive role in the Labour leadership contest through the endorsement of Ed Miliband – although the pair later fell out.