High Speed 2 (HS2) could be up to five times more expensive than its French equivalent according to a new academic study, reigniting rows over whether the £56bn railway plan is a “vanity project”.

The academics, led by Professor Tony May from Leeds University and transport consultant Jonathan Tyler, said that France's TGV line from Tours to Bordeaux was costing £20m per km, compared with a projected cost of around £105m per km for HS2.

The much higher unit cost of HS2 is due in part to the complex plan for London Euston and to the need for extensive tunnelling through the Chilterns Area of Outstanding Natural Beauty.

HS2 is conceived as a “transformational” rail project linking London, Birmingham, Leeds and Manchester, via 400km/h trains running on a dedicated twin track.

Britain's high speed rail line got the go-ahead in late March, after it passed through a Commons vote with 399 votes to 42.

Although the academics said they broadly support the high-speed rail line, they believe the only benefit it will achieve is to increase rail capacity, and will fall short of the other objectives to increase connections, regenerate the North and reduce impacts of climate change.

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"A fundamentally flawed vanity project"

The Institute of Economic Affairs (IEA) has also hit back at the government's handling of HS2.

"HS2 is a fundamentally flawed vanity project that will be extortionately expensive and deliver very little benefit to taxpayers. Belatedly, it seems that policymakers and academics alike are finally coming to this realisation," Mark Littlewood, director general at the IEA, said.

"The supposed justifications for going ahead with the project have been discredited one by one. Arguments about the benefits of faster journeys, capacity and regeneration of the north have all been debunked, and all this at the estimated cost of £80bn. Ultimately, if the HS2 project offered value for money the private sector would pay for it, rather than piling costs onto hard-pressed taxpayers," Littlewood added.

"Token cost-cutting will not suffice. The government should abandon the project altogether and look to prioritise removing regulations that are barriers to the development of commercially viable schemes that do not cost the taxpayer at all."

Britain's high speed rail line got the go-ahead in late March, but has frequently come under fire particularly on cost grounds. Jeremy Heywood, the head of the civil service, has been investigating HS2 in an effort to cut costly elements.

An HS2 spokesman said the French track was not comparable. He said: “The French track has no new stations; it does not go through a dense built-up urban area; it does not have the tunnels that we are building on HS2 to protect the environment‎ and property prices are very low in comparison to the UK. The net result is that it is cheaper.”

Professor May said yesterday: “What's needed is an independent, objective assessment of the alternatives. These would include a less damaging version of HS2, a better-connected new line from London and transport investment in the north rather than to the north.”

A report released in mid-May argued British cities and regions should seize the opportunity provided by HS2 to generate economic growth.

The study by the Independent Transport Commission found that there could be social and economic benefits brought by HS2, and that British cities should jump on the once-in-a-generation public infrastructure investment project to propel growth.

The government has said HS2 will cost £42.6bn to build, plus a further £7.5bn for the trains at 2011 prices.

In March, the government today announced it had shortlisted nine companies bidding for up to £11.8bn of work on HS2 for work between London and Crewe.