Sir Keir Starmer has come under fire from all sides after Labour suffered a crushing defeat in the Hartlepool by-election.
In a stunning result, the Conservatives took the seat – which had been Labour-held since it was formed in 1974 – with a majority of 6,940.
Boris Johnson hailed the outcome as “very encouraging” as the Conservatives appeared poised to make further gains in council elections across England.
Allies of the Labour leader acknowledged that it was an “absolutely shattering” blow as another pillar in the party’s once impregnable “red wall” crumbled.
They insisted however that Sir Keir would not be deflected from the course he had set out when he succeeded Jeremy Corbyn a little over a year ago.
However, there were calls from both the left and the right of the party for an urgent change of direction if they were to stand any chance of regaining power at the next general election.
On the left, former shadow home secretary Diane Abbott said it was not possible to blame Mr Corbyn for the setback and said Sir Keir needed to “think again” about his strategy.
Mr Corbyn himself said the results showed a loss of hope.
“We must offer a bolder vision to transform people’s lives and give them the confidence to strive for a more equal world,” he said.
Former shadow chancellor John McDonnell said the party had gone into the by-election “almost policy-less” and called for a return to a “real grassroots campaign”.
“We must never again send our candidates into an election campaign almost naked, without a policy programme, without a clear view on what sort of society you want to create,” he told the BBC.
Unite general secretary Len McCluskey said the loss was “staggering and worrying” and clear evidence that the strategy of the last year had not worked.
“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,” he said.
But there was criticism too from the right, including the Blairite former cabinet minister Lord Adonis.
He told the BBC: “The verdict of the people is the verdict of the people. The golden rule of politics is that you can’t avoid the verdict of the people.
“Clearly the public isn’t persuaded that Labour has either the leadership or the policies or the critique or the energy and the dynamism in terms of its view and we all need to consider that.”
The warning came as early results in council contests appeared to show voters deserting Labour, with the Tories taking Dudley, Redditch and Nuneaton and Bedworth councils in the Midlands, along with Harlow in Essex and Northumberland.
With results in from 17 out of 143 councils, the Conservatives had gained a total of 56 seats while Labour had lost 57.
In Hartlepool, the Conservative candidate Jill Mortimer gained 15,529 votes – more than half the total cast – with Labour’s Dr Paul Williams trailing on 8,589.
In her victory speech, Ms Mortimer said the result – overturning a Labour majority of more than 3,500 at the 2019 general election – was “truly historic”.
Visiting the constituency to celebrate, Mr Johnson said it was a mandate for the Government to press on with its plan to “build back better” after delivering on Brexit.
“What people want us to do now is to get on with delivering on everything else,” he said.
“Number one is continuing the vaccine rollout, making sure that we go from jab to jab, to jab to jobs, jobs, jobs.”
Shadow communities secretary Steve Reed said the Hartlepool result was “absolutely shattering” but insisted there is no going back on the strategy set out by Sir Keir.
“I’m very comfortable that we now have a leader that the country could see as an alternative prime minister – the problem is the Labour Party itself,” he told the BBC.
“What this shows is that, although we have started to change since the cataclysm of the last general election, that change has clearly not gone far enough in order to win back the trust of the voters.”
Votes are also being counted in the Scottish elections to Holyrood, where the issue of independence was a main feature of the campaign.
Scottish National Party (SNP) leader Nicola Sturgeon is pushing for a second vote on independence and the party is expected to emerge again as the largest party in the Scottish Parliament.
Results will also come in from Wales, where Mark Drakeford hopes to maintain Labour’s grip on the Senedd – but he may find himself forced to forge a new coalition to stay as First Minister.