The Labour mayor said “all options are on the table” when asked if legal action was a possibility if the prime minister pushes ahead and axes the Birmingham to Manchester high-speed rail route.
The Independent first revealed Mr Sunak was in secret talks – dubbed Project Redwood – with his chancellor Jeremy Hunt to scrap phase 2 of the project.
With a final decision delayed until after party conference, the PM and chancellor are thought to be considering an option to kick the northern leg into the long grass by delaying it by up to seven years.
Sharing his anger on Tuesday, Mr Burnham told GB News: “We are not just going to lie down and accept the way Whitehall has always treated the North of England.”
Asked if his authority could sue the government, the Labour mayor said: “All options would absolutely be on the table … We are fighting back. We’re getting organised. We’re not going to take things lying down, so they will be hearing from us.”
Mr Burnham added: “We don’t seek fights with Whitehall, but we know how to answer them back now and we’re not just going to lie down and accept the way Whitehall has always treated the North of England.”
The mayor said he had received “assurances” from the party – including Keir Starmer’s shadow transport secretary Louise Haigh – that a Labour government would build the northern leg. “We have a commitment.”
Mr Sunak is concerned about a lack of cost controls and high salaries at the company overseeing the project after he was shown figures suggesting the overall price could top £100bn, according to The Times.
A source familiar with the PM’s thinking told the newspaper that HS2’s finances were “far worse than anyone knows” and he was unwilling to “sit back and watch this balloon”.
Richard Bowker, the former Strategic Rail Authority head, told BBC Radio 4’s Today programme that scrapping the Birmingham-Manchester link would be “very stupid”. The industry expert also warned that failing to take the HS2 line into central London would be “utter madness”.
Birmingham Airport chief executive Nick Barton has written to the PM saying any move to ditch HS2 would be “a mistake” which would “short change every generation to follow”.
And the US owners of Birmingham City football club – in which NFL star Tom Brady holds a minority stake – warned Mr Sunak he will damage investor trust if he abandons the Birmingham to Manchester route.
In a letter reported by the Financial Times, the football club owners warned: “Any deviation could result in a loss of investor trust and this would have a considerable negative impact on the UK. The ambitious HS2 project falls into this category.”
Patrick McLoughlin, the ex-transport secretary, joined a chorus of senior Tories – including Boris Johnson, David Cameron and former chancellors George Osborne and Philip Hammond – in calling on the prime minister to build the project in full.
But several top Tories support moves to scale back the project, believing costs are out of control. Former leader William Hague said on Tuesday that HS2 has been “terribly badly managed” and is a “national disgrace”.
He told Times Radio: “It should have been cancelled a few years ago when it was clear that the whole thing was out of control.” He said there was now a “genuine dilemma” over whether it should go ahead “to at least complete and make sense of the parts that we can still do”.
Sir Gavin Williamson called for the rest of HS2 to be scrapped. In a blog post, the former minister said the “wheels have come off” the project and said the government should “stop this calamity while we can”.
Esther McVey told BBC Radio 4’s Today programme that “we certainly don’t” need the high-speed rail project to go to Manchester. The former minister said: “Thank goodness that the prime minister is looking at HS2’s spiralling cost.”
Tory minister Chris Philp confirmed on Sky News on Tuesday that Mr Sunak is reviewing how the cost of HS2 can be “controlled”, as he warned the price tag of the rail project has “roughly tripled” since its conception.
But the junior Home Office minister insisted that no decision has been made on whether to axe or delay the rail project’s northern leg.
Mr Philp insisted the people of the north are “definitely not” second-class citizens, as Mr Burnham claims they are being treated. “The commitment to the Midlands, the North, the levelling-up agenda is absolutely undimmed,” Mr Philp said.