Tony Blair has accused Keir Starmer, Andy Burnham and Wes Streeting of putting Labour’s future at risk by abandoning the centre ground, warning that the party’s “almost infinite capacity for self-delusion” means it is likely to lose the next election.

In a scathing 5,700-word attack on the prime minister and his would-be successors published on Tuesday night, Blair argued for the government to crack down on welfare spending, abandon restrictions on oil and gas and smooth relations with Donald Trump.

His essay, a highly unusual intervention for a past Labour prime minister, is likely to draw a furious response from across the party, where Blair’s legacy remains highly contentious. On Tuesday, one senior source accused him of abandoning social democratic values to embrace an agenda that had “no answers”.

But Blair also suggested it was a mistake for others in the party to seek to remove Starmer as prime minister, saying: “The Labour party is playing with fire; or, more accurately with its future, and that of the country. Whether there is a leadership change or not is irrelevant if it doesn’t start with a policy debate.

“Trying to force the prime minister out, before we know what policy direction we’re bringing in, is not a serious way of conducting ourselves.”

Blair attacked Burnham and his fellow leadership contender Wes Streeting – who has often been cast as a Blairite but rejects the label – for ideas on tax and spending that he said had been rejected by serious governments. He said it was a “perennial delusion” that the party should move left while losing seats to the right, saying it was “dangerous to do it in government”.

While Labour is likely to lose many more seats to Reform than the Greens in a general election, most analysts of the recent local elections suggest that it lost four times as many votes to the Greens, splitting the left-leaning vote.

Blair also criticised Starmer’s approach to the US war with Iran, despite most polls showing it was popular with the public – saying it was vital the US could trust the UK as an ally. He criticised cuts to international aid, which he said had weakened Britain’s influence, and said Starmer was trying to negotiate with Europe from a position of weakness.

The former prime minister named Angela Rayner’s employment rights bill and Ed Miliband’s net zero drive as key mistakes, alongside the phasing out of oil and gas licences and Rachel Reeves’ decision to raise the minimum wage and national insurance and change the status of non-doms. All of the policies had given “headwinds, not tailwinds to British business”, he wrote.

The government should now remove all obstacles to AI-related business growths, radically increase planning reform, reverse its North Sea energy policy and make fundamental changes to the welfare system, Blair argued, as well as seeking to repair relations with Trump’s White House.

“Without an agenda of this nature, radical but sensible, Britain will continue its long slide towards relegation from the Premier League of Nations,” he said.

A senior Labour source said: “Tony has evidently not been near a working-class Brit for decades but he’s clearly been away with the tech bro fantasists.

“Reheated Blairism has absolutely no answers to our national decline since the vultures were let loose. There was a time he would have stood up for social democratic values, but this shows just how far he has fallen.”

Blair said Starmer’s key issue was not a lack of charisma or communication but of grounding. “This is the defining problem of the government. Too often they seem to totter in the breeze. To lack ballast.”

The party should have ditched promises like the workers rights reforms and commitments on oil and gas licences in the early days of government, blaming the fiscal situation, Blair said, arguing that it would have won the goodwill of business. He also attacked the ending of the two-child limit, saying it was clear that welfare was in need of major reform.

But he was deeply critical of solutions proffered by those who seek to replace Starmer, saying Streeting’s modernising wing was “appearing to advocate rejoining the EU” as well as changes to capital gains that had been “rejected by successive governments for good reason”.

And he criticised Burnham’s alternative to adopt the “far-left critique about nothing good coming out of the last ‘40 years’ of ‘neoliberalism’, which presumably includes the last Labour government”.

Blair said it had been clear since the election that Starmer had been elected because of the distaste for the Conservative government, rather than on Labour’s offer, and that the party had no guiding vision from which its policies and politics could flow.

“The government is governing from an essentially traditional Labour ‘soft left’ position, parked firmly in the party’s comfort zone,” he said. “The government’s principal problem isn’t Keir’s personality. Or a failure to communicate ‘our achievements’. Or a need to assert more strongly Labour’s ‘values’.

“It is because we don’t have a worked-out, coherent plan for the country in a fast-changing world and are in the wrong political position from which we can devise one and win a second term.”

Blair – who was one of the strongest voices opposed to Brexit and a key player in calls for a new referendum – said he now believed that seeking to negotiate a new deal with Europe was nonsensical when Britain was in a weak position.

“Just as Brexit was never the answer to Britain’s challenges back in 2016, reversing it isn’t the answer to the country’s far worse situation in 2026.” He said any serious negotiation should only start when Britain is “at the farthest end of European competitiveness. At present, we’re not.”

He said that the UK’s position was immeasurably weaker than two decades ago – when the UK was a key US ally, a leader in Europe and a major player in the developing world because of international aid. “All are now in doubt or gone,” he said.

“What’s done is done. None of these things can simply be reversed. But to repair our standing, all require leadership and commitment.”