Ministers are now "actively considering" scrapping High Speed 2, amid growing concern that its budget could spiral out of control, according to a new documentary.

Senior government sources have claimed that ministers were "increasingly minded to kill off" plans for the £56 billion rail line and divert its budget to existing commuter routes.

The claims, which contrast sharply with Theresa May's public defence of the project, come in a Channel 4 Dispatches programme which also reports that annual spending on the scheme is due to rise by 40 per cent to £6 billion.

Separately, a Cabinet minister claimed that Mrs May initially wanted to "scrap the whole thing" after becoming Prime Minister, but "lacked the confidence, especially after losing her majority, to tackle the related vested interests."

The disclosures follow a series of articles by The Sunday Telegraph which revealed the increasing disquiet among ministers about the project, proposals to reduce the number of trains running along the route in order to help keep it within its budget, and plans to power the line with new onshore wind farms.

Last month Liz Truss, the Chief Secretary to the Treasury, wrote in this newspaper that the Government would "examine all major investment projects" as part of a spending review later this year, adding that ministers must be prepared to junk expensive "white elephant" projects that fail to provide "bang for buck".

A senior government source told Dispatches: "The costs are spiralling so much we've been actively considering other scenarios, including scrapping the entire project".

The source added that ministers "are increasingly minded to kill off the whole thing and put the money into upgrading the services used by millions of voters to get to work and back every day”.

Mrs May has publicly insisted that HS2 was needed to ensure "that we have the capacity that is needed on this particular route." Chris Grayling, the Transport Secretary, said the Government was "fully committed" to the project. More than £4.1 billion has been spent on HS2 since it was conceived a decade ago, with official figures indicating that spending is due to rise to an average of £4.2bn a year, for the next decade.

But, according to the Dispatches programme, which is due to air tomorrow [MON] evening, ministers now judge that “annual HS2 spending of up to £6bn a year will be needed”.

Meanwhile, in a letter sent last month to Mark Thurston, HS2's chief executive, Andrea Leadsom, the leader of the Commons, who campaigned against HS2 as a backbencher, has warned that her constituents "are increasingly concerned that the business case is being undermined from all angles, and the basis for which Parliament gave its support to the project may no longer exist."

Last week The Sunday Telegraph disclosed that David Lidington, Theresa May's de facto deputy, had asked HS2 to set out the "current business case" for the £56 billion project, after this newspaper revealed that the company had suggested it could cut the hourly number of trains by a fifth to prevent costs from spiraling out of control.

Mark Thurston, HS2's chief executive, insisted the project will go ahead.

“HS2 will be transformational to jobs and prosperity across the North and the rest of the country - that’s the prize and now we need to hold our never and deliver it,” he said. “Our job is to build this railway for £56bn and this is what we will do, until the government advises us otherwise."

A Downing Street spokesman said the claim that Mrs May had wanted to scrap HS2 was "categorically untrue".

The Department for Transport added: “HS2 is already underway with 7,000 people and 2,000 businesses working on building what will become the backbone of Britain’s rail network.

“This new rail line will integrate with Northern Powerhouse Rail and together they will transform the region, improving connections between major cities, boosting productivity, delivering better journeys for passengers and driving forward economic growth across the country.”