The High Speed 2 project was meant to revolutionise rail travel in the UK, slashing journey times and reducing carbon emissions.
But Europe’s largest infrastructure project has become synonymous with delays, soaring costs and government incompetence.
Rishi Sunak now finds himself embroiled in a major row with his own party amid speculation that the final leg of the project may be scrapped.
Here, HuffPost UK looks at what the project is, and how we ended up here.
Why is it called HS2?
HS2 is the follow-up to High Speed 1, which is the line between London and Kent connecting the UK to routes on the European continent - otherwise known as the Eurostar.
What was the purpose of it?
It was initially intended to link London and the West Midlands, with a further phase extending to cities in the North. The main destinations would be Birmingham, Manchester and Leeds.
The plan came in response to calls for the government to close the north-south divide and spread the UK’s wealth more equally across the whole country, rather than it being concentrated in London and the south east.
The aim was to run 18 trains an hour in each direction to and from the capital - at speeds of up to 224mph - compared to between two and six an hour on HS1.
Whose idea was it?
The idea was first proposed by the last Labour government in 2009.
Then transport secretary Geoff Hoon set up HS2 Ltd, the company tasked with examining the potential for a new high-speed line.
The following year, the Department for Transport set out plans for a Y-shaped network connecting London with Manchester and Leeds.
What was the initial plan?
HS2 would be built in two phases, with the first section connecting London and Birmingham by 2020 and cost £7bn.
The second phase would go from Birmingham to Manchester Airport and Manchester Piccadilly in the west, and to Leeds in the east.
The initial end date was 2033, with a total cost of around £35bn.
In 2013, MPs voted by 451 to 50 to give the project the green light.
How has it gone since then?
Er, not terribly well.
Work on the project began in 2020 with tunnelling under the Chiltern Hills on the edge of northwest London, but it has been beset by problems ever since.
The north eastern leg to Leeds was scrapped in 2021 due to rising costs, prompting Labour to accuse the Tories of a “great train robbery” and of betraying voters in the north.
Unbelievably, it has also been reported - and never denied by ministers - that the line will not even reach Euston Station in central London, but will instead begin at Old Oak Common in the west of the city.
And now there is increasing speculation that Rishi Sunak and his chancellor, Jeremy Hunt, are set to axe the Birmingham to Manchester leg of the project to save money.
Former transport secretary Grant Shapps has added fuel to the fire yesterday by refusing to confirm the second phase of the project will go ahead.
And the prime minister himself did little to dispel the growing belief that the project, which was meant to improve connectivity between the capital and the north, will end up going only as far as Birmingham.
What is the latest estimate of the cost?
The initial estimate of £35 billion had already risen to £55.7bn by 2015, and has continued to spiral ever since.
The government’s most recent official estimate in 2019, which excluded the cancelled Leeds leg, was around £71bn.
Since then, no official estimates have been made, but experts say the figure could be around £180bn.
About £25 billion of taxpayers money has already been spent on the project.
What happens next?
Your guess is as good as ours.
Even if Sunak opts to go ahead with the Manchester leg, the political damage done to the government’s reputation for handling major infrastructure projects is enormous.
Manchester mayor Andy Burnham told Sky News yesterday that people in the north are being “treated like second class citizens”.
Meanwhile, civil war has erupted in the Conservative Party, with senior figures including George Osborne, Boris Johnson and Lord Heseltine expressing their concerns about the proposed curtailing of the project.
Handily, this year’s Tory conference kicks off on Sunday in, of all places, Manchester.
Surely they wouldn’t be mad enough to announce that HS2 will no longer make it to the city in advance of his party’s annual jamboree?
Then again, we never know...