Andy Burnham says the north will be left with "Victorian infrastructure" if the Birmingham to Manchester HS2 line was scrapped.
Northern leaders have blasted the Government for "keeping them in the dark" after reports Rishi Sunak may be considering scrapping the Birmingham to Manchester HS2 rail line.
Under growing pressure, the Prime Minister has refused to be drawn on the direction of the multi-billon pound rail project - but insisted he is committed to levelling up.
But Andy Burnham has accused Mr Sunak of "leveling down", telling ITV News that if plans were scrapped it would leave the North with "Victorian infrastructure".
Writing in a letter to the Prime Minister on Monday, Mr Burnham and leader of Manchester City Council, Bev Hughes, said: "We are becoming increasingly concerned about the rumours swirling around HS2 to Manchester and, by extension, Northern Powerhouse Rail (NPR)."
They said the current plan would have "massive ramifications" for both Manchester and the rest of the North and the Midlands.
Mr Burnham and Ms Hughes went on to say it's deeply "disrespectful to our residents and businesses" that they have been unable to share their views on this or have not been given any information about what is being considered, adding "we are completely in the dark".
The Greater Manchester Combined Authority are asking for the Prime Minister for a meeting before any final decision is taken.
They finished the letter adding: "If you refuse to accept any of what we are saying, we believe that people here will conclude that your promises to level up the North, on which this Government was elected, are utterly meaningless."
Meanwhile, Rishi Sunak has been warned by senior Tories not to scrap the line ahead of the Conservative conference in Manchester.
Cabinet minister Grant Shapps said it would be "crazy" not to reconsider the project in the light of the rising price tag and the UK's economic situation.
But former chancellor George Osborne and ex-deputy prime minister Lord Heseltine warned that axing the Manchester route would be a "gross act of vandalism" which would mean "abandoning" the North and Midlands.
Writing in The Times, they warned Mr Sunak: "Governments are remembered for what they build and create. Make this mistake and yours may only be known for what it cancelled and curtailed."
If the northern section was cancelled "the remaining stump, little more than a shuttle service from Birmingham to a London suburb, would become an international symbol of our decline", they said.
Commons Health Committee chairman Steve Brine said it would look "odd" to scrap the scheme in the days before Tory MPs and activists arrive in Manchester.
He also said he hoped the line would run all the way into central London rather than terminating at Old Oak Common in the capital's western suburbs.
The Sunday Telegraph reported the potential cost of the high-speed rail scheme - which Chancellor Jeremy Hunt has said is "out of control" - had increased by £8 billion just for the initial London-Birmingham stretch, up from £45 billion.
Downing Street and Treasury insiders suggested no timing had yet been fixed for any announcement on the future of the scheme.
But the Prime Minister and Chancellor are reported to be meeting to discuss the situation in the coming days.
Former transport secretary Mr Shapps used broadcast interviews on Sunday, 25 September, to say the Government could not write an "open-ended cheque" if costs were "inexorably going higher and higher".
In a hint that a delay rather than an outright cancellation could be an option, Mr Shapps said: "I think the sequencing of what happens next is a perfectly legitimate question."
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