Image source, HS2/PA
By Nick Edser
Scrapping the HS2 rail link to Manchester would be a "gross act of vandalism", the former chancellor, George Osborne, has said.
Writing in The Times, Mr Osborne and Lord Heseltine said cancelling the extension would be an "act of huge economic self-harm".
The government has refused to guarantee that the high-speed line will continue between Birmingham and Manchester.
The BBC understands a decision on HS2 could be made as soon as this week.
At the weekend, Grant Shapps, the current Defence Secretary and former Transport Secretary, said it would be "crazy" not to review plans for HS2 given how costs have soared.
He told the BBC that the Ukraine war and a spike in inflation meant any government would need to make "serious decisions" on affordability.
HS2 is intended to link London, the Midlands and the north of England - the first part, between west London and Birmingham, is in mid-construction.
But the scheme as a whole has already faced delays, cost increases and cuts - including to the planned eastern leg between Birmingham and Leeds.
The last official estimate on HS2 costs, excluding the cancelled eastern section, added up to about £71bn.
Chancellor Jeremy Hunt said last week that costs were getting "totally out of control".
However, in The Times, Mr Osborne and Lord Heseltine said scrapping the route to Manchester, and potentially the link between west London and Euston station, would be "an act of huge economic self-harm, and be a decision of such short-sightedness that we urge the prime minister: don't do it".
"How could you ever again claim to be levelling up when you cancel the biggest levelling-up project?", they ask.
"It is difficult to conceive of a more damaging decision than cancelling a project that has been promised by six different British governments.
"Where would a cancelled HS2 leave the North and Midlands? Abandoned is the answer."
Speaking to the BBC's Today programme, the Mayor of Greater Manchester, Andy Burnham, said scrapping the HS2 extension "rips the heart" out of the rail plans for the Northern Powerhouse Rail project.
"It would leave the north of England with Victorian infrastructure probably for the rest of this century," he added.
If that happened while infrastructure in the south is upgraded it "is a recipe for the north-south divide to become a north-south chasm, the very opposite of the levelling up that we were promised in this Parliament," Mr Burnham said.
Labour has so far refused to confirm it would fund the HS2 line to Manchester if the Conservatives axe it.
On Sunday, Darren Jones, new shadow chief secretary for the Treasury, said the Labour party would "love to build the HS2", but said little "proper" information had been made available by the government.
Also at the weekend, more than 80 companies and business leaders also sought clarity over the commitment to HS2.
The bosses of dozens of businesses and business groups - including Manchester Airports Group, British Land, Virgin Money, and the Northern Powerhouse - all signed a letter to the government urging renewed commitment to HS2, saying that repeated mixed signals were damaging the UK's reputation and the wider supply chain.
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