Shadow business secretary Rebecca Long-Bailey has joined the race to become Labour leader, saying the party needs a “proud socialist” to succeed Jeremy Corbyn.

With nominations due to open on Tuesday, Ms Long-Bailey – favourite of the Labour left – said she could be trusted to maintain “our socialist agenda”.

Her comments will be seen as a thinly veiled swipe at shadow Brexit secretary Sir Keir Starmer, who has been keen to stress his left-wing credentials despite being seen to come from a more centrist tradition.

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Writing in the Tribune magazine, she said: “Many candidates in the leadership election say they will not return to the triangulation and Tory-lite policies that held our party back before Jeremy.

“But we need a leader that can be trusted with our socialist agenda. A leader who is totally committed to the policies and has the political backbone to defend them.

“We need a proud socialist to lead the Labour Party, driven by their principles and an unwavering determination to see democratic socialism in our lifetime.

“For all of these reasons and more, I have decided to stand for election to become the next leader of our party.”

Party chairman Ian Lavery immediately announced he would not be standing and would be backing Ms Long-Bailey.

“We must ensure that we never again are seen to be taking working class communities for granted or to write them off as ignorant or ill-educated,” he said in another apparent jibe at pro-Remain contenders.

Ms Long-Bailey’s announcement came as the party’s ruling National Executive Committee (NEC) set out the timetable for election, with the new leader to be announced at a conference on Saturday April 4.

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The NEC also confirmed that, as in 2016, “registered supporters” will be able to vote if they pay a £25 fee.

A party spokeswoman said there would be a 48-hour window to apply from 5pm Tuesday January 14.

“We are by far the largest political party in the UK with well over half a million members,” the spokeswoman said.

“We want as many of our members and supporters to take part, so it has been designed to be open, fair and democratic.”

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Under the terms of the contest, candidates need to secure the nominations of least 10% (22) of the party’s MPs and MEPs.

Those who succeed will go forward to the second stage where they must get the nominations of 5% of constituency Labour parties or three Labour affiliates – of which at least two must be trade unions – comprising at least 5% of the fully paid-up affiliate membership.

(PA Graphics)(PA Graphics)

The closing date for new members to join and be eligible to vote will be January 20 in the postal ballot.

This marks a change from the last election in 2016 when a retrospective cut-off date was set.

Under the timetable set out by the NEC, nominations from MPs and MEPs will open on January 7, closing at 2.30pm on January 13.

The second stage of nominations from constituency parties and affiliates then opens on January 15 and runs to February 14.

The ballot of members and registered supporters opens the following week on February 21, closing at midday on Thursday April 2.

The same rules and timetable will apply to the contest to succeed Tom Watson as deputy leader.

Labour Jeremy Corbyn leaves the Labour NEC meeting which agreed the timetable for the leadership contest (Dominic Lipinski/PA)

In addition to Ms Long-Bailey and Sir Keir, four other candidates have announced they intend to stand for the leadership – frontbenchers Emily Thornberry and Clive Lewis, and backbenchers Jess Phillips and Lisa Nandy.

Former cabinet minister Yvette Cooper has ruled out a leadership bid.

Ms Cooper, who stood against Mr Corbyn in 2015, said: “The scale of Labour’s defeat challenges our whole party not just the next leader.

“I’m not standing for Labour leader this time but I’ll keep fighting for a Labour government.”