Sir Keir Starmer will launch his Labour leadership campaign with a pledge to win back former supporters who switched to the Tories at the general election.
At a launch event in Manchester on Saturday, the shadow Brexit secretary will say the party must retain its radicalism while making it relevant to people’s everyday lives.
He will promise to pursue Boris Johnson relentlessly in Parliament if he succeeds in becoming leader when the result is announced in April.
Sir Keir has emerged as the clear favourite among Labour MPs and was the first of the six contenders to secure the 22 nominations required to progress to the next stage of the contest.
Sir Keir has emerged as the clear favourite among Labour MPs and was the first of the six contenders to secure the 22 nominations required to progress to the next stage of the contest.
Shadow business secretary Rebecca Long-Bailey, the favourite of the left of the party, and the backbenchers Lisa Nandy and Jess Phillips have also passed the threshold.
However shadow foreign secretary Emily Thornberry, with 10 nominations, and Clive Lewis, with just four, appear to be struggling. They have until 2.30pm on Monday to get the necessary support or they will be forced to drop out. 
They have until 2.30pm on Monday to get the necessary support or be forced to drop out.
Despite his lead, Sir Keir has been keen to emphasise his radical credentials in a pitch to grassroots party members who are thought to be more left-wing than the MPs and whose votes will ultimately determine the outcome.
‘Focussing tirelessly on getting Labour back into government’
Speaking ahead of the launch, he said: “The challenge for Labour today is to defend our values, retain our radicalism, and to make that relevant to people’s everyday lives.
“People desperately need and want us to win.
“We have to deliver a programme that will tackle low pay and insecure work, rebuild our public services, empower communities and tackle the climate emergency.
“We have to rebuild people’s trust in Labour as a force for good and real change.”
He said the party needed to set its sights on winning back the support of voters across England, Scotland and Wales who turned away from it at the election in December.
“Boris Johnson said that many voters in the North had lent their votes to the Conservatives.
“We must set ourselves the task of winning those votes back,” he said.
“If elected leader, I will pursue Boris Johnson relentlessly in Parliament.
“We will connect our opposition in Parliament to Labour’s mass movement and to the wider forces in our country who do not want five more years of Tory misrule.
“And we will bind that together with an electoral strategy that focuses tirelessly on getting Labour back into government.”
Starmer says Jeremy Corbyn positioned Labour in the right place against austerity
Sir Keir would not be drawn into personal criticism of Jeremy Corbyn on BBC 1’s Breakfast programme ahead of his Saturday launch, although he said that it was right that he was now stepping down after Labour’s “devastating” general election defeat.
Unlike Rebecca Long-Bailey, who gave Mr Corbyn 10/10 and Ms Thornberry who gave him 0/10, Sir Keir refused to give him marks out 10 for his leadership.
“Jeremy Corbyn led us through really difficult times as a Labour Party. He positioned us in the right place on anti-austerity but we lost the election and now he is stepping down. That is the right thing to do,” he said.
“I am not going to get into ranking Jeremy Corbyn out of 10. I think it trivialises him. He is a friend and a colleague. I respect him, thank him for what he has done, but we are moving on now.”
When asked about tackling anti-Semitism, he pledged to take personal charge of dealing with the issue. “There has to be leadership from the top and a personal involvement in this,” he told BBC Breakfast. “I never want our activists, our members, our supporters, ever to knock on a door again and to be met with the response: ‘I usually vote Labour but I’m not going to do so because of anti-Semitism.’”
Union support for Sir Keir Starmer
Sir Keir has been keen to emphasise his radical credentials in a pitch to grassroots party members who are thought to be more left-wing than Labour MPs and whose votes will ultimately determine the outcome of the contest.
He dismissed suggestions that he was too “centrist” to succeed. “I want the Labour Party to be radical in the sense that we need fundamental change. Frankly, I find all the labels just get in the way,” he said.
Unison’s backing of Sir Keir has provided him with momentum at the start of the campaign.
The decision was taken by the union’s Labour Link committee, which is made up entirely of Labour members.
General secretary Dave Prentis said: “This is a pivotal time for Labour.
“We believe – if elected by the membership – Keir Starmer would be a leader to bring the party together and win back the trust of the thousands of voters who deserted Labour last month.
“Keir has a clear vision to get Labour back to the winning ways of the past.
“He is best placed to take on Boris Johnson, hold his Government to account and ensure Labour can return to power and once more change working people’s lives for the better.”