Sir Keir Starmer’s leadership of Labour has come in for heavy criticism from prominent figures across the party following the Hartlepool by-election humiliation.

From the left, former shadow cabinet minister Richard Burgon said Labour needed to “urgently change direction”.

But while Sir Keir may have expected hostile fire from allies of former leader Jeremy Corbyn, some of the most stinging criticism came from Blairite grandees who had previously supported him.

Former cabinet minister Lord Adonis hit out at the “waffle” from the present leadership and said that while he had backed Sir Keir, he now viewed him as a “transitional” figure.

“Labour’s problem is that it has had weak or terrible leaders since Tony Blair stood down 14 years ago, and until it gets an electable leader it will keep losing elections,” Lord Adonis wrote in The Times.

He said he had hoped Sir Keir would have the ability to reshape Labour but “unfortunately, he turns out to be a transitional figure – a nice man and a good human rights lawyer, but without political skills or antennae at the highest level”.

Giving a bleak assessment of Labour’s future, he warned that if it suffered a fifth successive general election defeat “there may not be much of a Labour party left, and some other political vehicle — maybe a populist one — could seize the anti-Conservative cause in England”.

Former Hartlepool MP Lord Mandelson, a key figure in the New Labour era, sought to blame the legacy of Mr Corbyn’s leadership and the Covid-19 pandemic for the by-election defeat.

“We have not won a general election in 16 years,” he told BBC Radio 4’s Today.

“We have lost the last four, with 2019 a catastrophe – the last 11 general elections read: lose, lose, lose, lose, Blair, Blair, Blair, lose, lose, lose, lose.

“We need for once in this party to learn the lessons of those victories as well as those defeats, and I hope very much that when Keir and his colleagues in the shadow cabinet say this means that we have got to change direction that they actually mean it.”

Khalid Mahmood, a former shadow defence minister, lashed out at the “London-based bourgeoisie, with the support of brigades of woke social media warriors” that has “effectively captured the party”.

The Birmingham Perry Barr MP – who quietly quit his frontbench role last month without any announcement – said voters in former heartlands viewed Labour as “a party that has lost its way”.

Hartlepool was held by Labour in 2019 despite the damage done by Boris Johnson to the “red wall” of seats in the party’s northern heartlands.

Winning back those voters is a key task for Sir Keir but left-wing allies of former leader Mr Corbyn questioned whether he would be able to do it.

Mr Corbyn himself, who was effectively thrown out of the Parliamentary Labour Party by Sir Keir, said: “We must offer a bolder vision to transform people’s lives and give them the confidence to strive for a more equal world.”

Mr Burgon, who served in Mr Corbyn’s shadow cabinet, said: “We are going backwards in areas we need to be winning.

“Labour’s leadership needs to urgently change direction.

“It should start by championing the popular policies in our recent manifestos – backed by a large majority of voters.”

Former shadow chancellor John McDonnell said Labour’s lack of policies meant candidates were being sent “almost naked” into election battles.

“Keir now needs to sit down and think through what happened in this campaign, and what I’ve been saying to him is you need to demonstrate to people the sort of society you want to create, the policy programme that will achieve that society, and you need to get back to that real grassroots campaign,” he told the BBC.

Len McCluskey, general secretary of the Unite union which helps bankroll Labour, said the Hartlepool loss was “staggering”.

“The strategy of the last year has not worked,” he said.

“Disconnection from our heartland communities will only deepen unless they can look at Labour and see a party with clear, bold policies that understands and speaks for them.”

The scale of the loss in Hartlepool – the Conservative candidate Jill Mortimer gained 15,529 votes, more than half the total cast, with Labour’s Paul Williams trailing on 8,589 – and setbacks in council elections underlined the challenge facing Sir Keir.

The Labour leader promised to do “whatever it takes” to rebuild trust in the party.

A shake-up of his shadow cabinet is widely expected in Westminster, but Sir Keir acknowledged “this goes way beyond a reshuffle or personalities”.

He said Labour needs to “stop quarrelling among ourselves”.

But with votes still being counted across the country, Sir Keir may have to brace himself for further criticism before the weekend is out.