Shadow Brexit secretary Sir Keir Starmer has warned Labour must not “oversteer” away from the left wing politics of Jeremy Corbyn in the wake of the party’s crushing general election defeat.

Sir Keir, who confirmed he was “seriously considering” a run for the leadership, said Mr Corbyn had been right to make Labour an “anti-austerity” party.

In a clear attempt to distance himself from the legacy of Tony Blair, he said the party could not afford to go back to “some bygone age”.

His intervention came as the former prime minister delivered a crushing verdict on Labour’s election performance, saying the party had gone into the contest with a “strategy for defeat”.

Tony Blair, delivering a speech in London, has blamed Jeremy Corbyn for Labour’s election defeat (Yui Mok/PA)

In a speech in London, Mr Blair laid the blame firmly at the door of Mr Corbyn, saying he had pursued a policy of “almost comic indecision” on Brexit which managed to alienate both sides of the debate.

“I believe with different leadership we would have kept much of our vote in traditional Labour areas,” he said.

“He (Mr Corbyn) personified politically a brand of quasi-revolutionary socialism, mixing far left economic policy with deep hostility to Western foreign policy which never has appealed to traditional Labour voters and never will appeal to them, and represented for them a combination of misguided ideology and terminal ineptitude that they found insulting,” Mr Blair said.

Mr Corbyn came under fierce attack when he addressed a meeting of the Parliamentary Labour Party on Tuesday, with a number of MPs angrily blaming him for their worst election performance since 1935.

However, Sir Keir, who is seen as coming from a more centrist tradition than the Labour leader, said it would be a mistake to simply abandon his radicalism.

“What Jeremy Corbyn brought to the Labour Party in 2015 was a change in emphasis that was really important – a radicalism that matters,” told the BBC Radio 4 Today programme.

“We need to build on that rather than simply say ‘Let’s now oversteer and go back to some bygone age’. We need to build on that radicalism.

“What we mustn’t do is say now, because we have lost in 2019, that move to an anti-austerity party has got to be rejected and we go back to some other political place that we were in in the past.”

Sir Keir’s comments will be seen as a pitch to win support from left wing grassroots members who propelled Mr Corbyn to the leadership in 2015 and who remain a significant force within the party.

Currently shadow business secretary Rebecca Long-Bailey is regarded as the favourite of the Labour left to succeed Mr Corbyn, who has said he will stand down early next year.

Sir Keir insisted as leader he would make his own decisions rather than simply following in the footsteps of one of his predecessors.

Yvette Cooper said Labour needed to win back ‘patriotic’ older voters (Danny Lawson/PA)

“I don’t need somebody else’s name tattooed to my head, some past leader, in order to identify and make decisions. I can make them for myself,” he said.

He rejected suggestions that as a north London lawyer who strongly supported Remain, he was too middle class to get elected.

“My dad worked in a factory, he was a toolmaker, and my mum was a nurse, and she contracted a very rare disease early in her life that meant she was constantly in need of NHS care,” he said.

“So, actually, my background isn’t what people think it is. I know what it’s like.”

Meanwhile the former cabinet minister Yvette Cooper said she was also considering a leadership bid, having unsuccessfully stood against Mr Corbyn in 2015.

She suggested the party needed to move away from the politics of both Mr Corbyn and Mr Blair if it was to win back the support of “patriotic” older voters who abandoned it for the Tories.

“We cannot just become a party that is concentrated in cities with our support increasingly concentrated in diverse young fast-moving areas while older voters in towns think we aren’t listening to them,” she told the Today programme.

“That is not a left-right issue, and this is where both the Jeremy Corbyn and Tony Blair challenge comes in, because both the left and the right of our party are seen as internationalist, not patriotic, at the moment.

“That might not be fair, but it is how they are seen. We should be able to be both patriotic and outward-looking.”

In his speech, Mr Blair said Labour’s election performance had been “unforgivable” and that change was essential if the party was to survive.

“The result has brought shame on us. We let our country down,” he said.

“The choice for Labour is to renew itself as a serious, progressive, non-Conservative competitor for power in British politics, or retreat from such an ambition, in which case over time it will be replaced. That is the starkness of the position.”