Labour's lurch to the Left is pushing Britain into the 'relegation' zone, Tony Blair has warned.

In a damning assessment, the former prime minister said the party has retreated into a Left-wing 'comfort zone', with ministers more interested in increasing welfare than boosting the economy.

Sir Tony said Labour had no 'coherent plan' for transforming Britain, leaving ministers to 'totter in the breeze' instead of leading the country.

He dismissed the idea that ditching Keir Starmer would transform the government's fortunes, saying that changing the leader would be 'irrelevant if it doesn't start with a policy debate'.

In a warning to Sir Keir's leadership challengers, he said that moving 'even further Left' is doomed to fail.

Sir Tony said that Labour will lose the next election unless it adopts 'radical' policies, including ditching Ed Miliband's Net Zero drive, working with the Tories to cut welfare and doing 'whatever it takes' to stop the boats.

'The Labour Party is playing with fire,' he said. 'Or more accurately, with its future and that of the country'.

He added that unless Labour changes course 'Britain will continue its long slide towards relegation from the Premier League of Nations'.

But, in a sign that he fears the government will get dragged Left-wards by Labour's civil war, he said the party has an 'almost infinite capacity for self-delusion'.

Sir Tony, who famously championed the idea of 'New Labour', said that Sir Keir's failure to choose between old and new had left him leading a party governing as 'Just Labour' where it 'risks being sliced to the Left and Right of itself'.

His comments came in a 5,600-word essay on Labour's future, which delivers a withering verdict on Sir Keir's first two years in office.

The intervention comes at a time when the government is paralysed by Labour infighting.

Almost 100 Labour MPs have called for Sir Keir to resign in the wake of this month's disastrous local election results. Wes Streeting has said he will trigger a leadership challenge after quitting the Cabinet and Andy Burnham is expected to join any contest if he wins next month's Makerfield by-election.

But Sir Tony warned that Labour's problems run much deeper than Sir Keir's insipid leadership, saying that successful governments 'don't start with a personality contest'.

'Whether there is a leadership change or not is irrelevant if it doesn't start with a policy debate,' he said. '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.'

Sir Tony took a swipe at Mr Burnham, saying his criticism of '40 years of neoliberalism' in Britain 'presumably includes the last Labour government'.

And he attacked Wes Streeting's plan for a so-called 'wealth tax' saying the idea of equalising capital gains and income tax has been rejected by successive governments 'for good reason'.

But he reserved his fiercest criticism for Sir Keir, saying Labour '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'.

Sir Keir fought the election on a promise of change, but has ended up 'parked firmly in the party's comfort zone,' Sir Tony said.

He added: 'In the last Budget, it appeared as if we were increasing tax to pay for additional welfare spending, when the public already thinks welfare bills are too high.'

Labour's attempt to trim £5billion from the welfare bill ended in failure last year when Sir Keir caved in to Left-wing rebels within the party.

Sir Tony urged the PM to outflank them by taking up Kemi Badenoch's offer to work together on cutting welfare, saying: 'By the end of this decade, we could be spending more on incapacity and disability than on defence. No serious country can do that.'

He also called on Labour to ditch much of its current economic policy, saying that measures such as 'the new workers' rights laws, the Net Zero acceleration and phasing out of the British oil and gas industry, the uplift in the minimum wage beyond inflation, and the Non Dom changes' have given 'headwinds not tailwinds to British business'.

He added: 'The PM and Chancellor should have said right at the outset: these are commitments which economic circumstances have rendered unwise to proceed with. The priority is growth.'

The Chancellor's decision to impose a £25billion National Insurance hike in her first Budget 'compounded the problem' and left employers feeling they faced an anti-business government.

Sir Tony, who was a leading opponent of Brexit, warned leadership contenders such as Mr Streeting and Mr Burnham that 'reversing it isn't the answer'.

He said Britain could only ever get a decent deal if it is able to negotiate from a 'position of economic strength'.

And he said it would be 'impossible' for the UK to go back fully into the EU while it remains 'essentially hostile' to technological innovation, which he says will transform the world.

Sir Tony set out a ten-point plan for governing from the 'radical centre'.

Ideas include prioritising 'cheaper energy and electrification over Net Zero and (using) what is left of our North Sea oil and gas resources' – something he says is 'essential for our competitiveness'.

He called for sweeping reforms to a welfare system which 'at points incentivises people not to work'.

And he said ministers should do 'whatever it takes' to tackle the illegal migration crisis, warning that doing so is a 'precondition' to making the argument that some immigration is essential for growth.

Outside experts should be appointed as ministers in a 'reimagined state' in which 'taxes and spending can be lower, productivity higher and Government seen as enabling not directing'.

Sir Tony also warned that Labour will have to work hard to rebuild relations with the United States after Sir Keir snubbed Donald Trump's initial request to use British bases to launch attacks on Iran – a decision he says was 'not the best way to treat our ally'.

Mr Trump's second presidency, he said, represents 'less a "rupture" than a "reckoning."'

'This side of the water we're being told some home truths which, if wise, we will wake up to,' he said. 'Europe needs to build economic competitivity and military capability. At present it is not succeeding in either as it should.'

Downing Street declined to comment.