HS2 creator says Rishi Sunak must not cut ‘the most important part'

“If you're going to build a new railway it's got to connect the principal cities in the North, the Midlands and the South,” he said. “Otherwise, it's just joining up two cities which are already fairly well connected. What’s the point in that?

“Once you start lopping limbs off the whole thing suffers because you've no longer got the legitimacy that you're connecting eight of the top 10 city regions in the country.”

It comes as Prime Minister Rishi Sunak is considering plans to scrap the second phase of HS2 – due to link Birmingham and Manchester by 2035 at the earliest – amid concerns about rising costs.

After the Leeds leg was axed official estimates suggested HS2 could cost up to £71bn. But that figure, set in 2019 prices, is expected to rise to more than £90bn when it is revised later this year.

Professor McNaughton said costs have spiralled because the project has been drawn out and delayed on numerous occasions and too much is being spent on salaries for the “enormous white collar army”.

“You want to do it as quickly as possible,” he said. “If you do it slowly the overheads just build up.

“Where does the money go? It doesn’t go into steel and concrete. It goes into contracts and to project managers and designers.”

He added: “It needs a serious reset and it needs to get back to the slim programme we had a number of years ago.”

Forty-four people working for HS2 Ltd, the taxpayer-funded company which runs the project, were each paid more than £150,000 in 2022/23. Their combined pay was £8.8m.

HS2 was first proposed by Gordon Brown’s Labour government in 2009 and Professor McNaughton said “the early years of the scheme were really quite efficient”.

He also said “the pressure was on” to finish Phase 1, from London to Birmingham, by 2026 and ensure lines reach Manchester and Leeds by 2033 but progress stalled.

“The political support got distracted by other things,” he said. “You have to keep making the case for it.

“The second thing is people keep fiddling with it and every time someone chucks away the design and starts again you lose time.”

Professor McNaughton said contractors are being asked to shoulder all of the risk, so they are inflating their prices so they can take out expensive insurance cover.

“When you do a project like this things happen,” he said. “Somewhere there will be poor ground conditions, bad weather or political change.

“They increase their prices by hundreds of millions of pounds because they can't afford to take the risk. What happens in other countries is the government takes the risk over the things that the contractor can't influence.”

Douglas Oakervee’s review of HS2, published in 2020, found the full Y-shaped route with legs to Manchester and Leeds would cost £108bn, but it would deliver at least £1.30 of benefit for each pound of public money spent.

The review also warned the costs would exceed the benefits if the final bill exceeded £138bn.

The Government has previously been accused of mismanaging HS2 and causing the overall cost to rise with a series of delays, reviews and design changes.

In March, Mr Harper announced that the Birmingham to Crewe stretch of HS2 would be delayed by two years to spread out spending after inflation caused costs to rise significantly.

The National Audit Office (NAO) warned the move “could lead to an overall increase in spend in the long term”.

Mr Harper also said the Government was pausing construction work on a new HS2 station in Euston for two years, so it could save money and come up with new designs.

Trains are now not expected to run into Euston until 2041 at the earliest after initially being scheduled for 2026, and the cost is predicted to balloon from £2.6 bn to £4.8bn.

The latest official estimate states Phase 1 of HS2, which will link the West Midlands and London, is expected to cost up to £44.6bn and open between 2029 to 2033.

Phase 2a, linking West Midlands to Crewe, is due to be delivered between 2030 and 2034, and cost up to £7bn. Phase 2b, linking Crewe and Manchester, is expected to cost up to £22bn and open between 2035 to 2041.

Ministers appeared to scrap the eastern leg to Leeds in 2021 to save money – but the Department of Transport is currently conducting a study which will look at whether HS2 services can run to the city via another route.