THE Government have been attacked by High Speed 2 campaigners after two undisclosed reports came to light throwing the value of the £33bn project seriously into doubt.

Documents recently released via the Freedom of Information Act revealed officials had been sitting on information since 2009 which showed the purported benefits were hugely exaggerated.

HS2 Action Alliance has branded the Coalition 'irresponsible'.

The campaign group has taken out a large advert in The Spectator magazine criticising the apparent suppressing of the information.

A key argument for the high speed line through the Chilterns has been that it will save crucial time for busy businessmen, assuming time spent travelling is wasted.

Anti-HS2 figures have protested since the start that with modern technology such as laptop computers, this assumption is flawed.

Now, the newly released Department for Transport documents from 2009 show that the ‘value of time’ figures used to calculate the returns from HS2 should be halved and their figures are ‘unsupportable’.

Researchers found that actually virtually no extra work would be produced by HS2 because of technology.

They told officials to change their '1960s' approach to their calculations.

Having conducted extensive studies they found the large majority of business travellers did some work on train journeys and almost half of businessmen's travel time was spent working.

The report added: “"Sixty per cent reported that they would do no work in the 'saved' time."

HS2 Action Alliance said more than 40 per cent of the projected monetised benefits of HS2 come from assuming businessmen do not work on trains.

Hilary Wharf, Director HS2AA, said: “It is at the very best irresponsible of Government to have hidden the report’s findings from consultees back in 2011 and the various committees that have all investigated HS2.

“Allowing for the recommended halving of the value of time and using the DfT’s own figures HS2 now delivers a Benefit Cost Ratio of just 90p. This means HS2 loses money for every £1 of taxpayers’ money spent.

“This is a £33bn transport project, the biggest for a generation, and yet these reports show its business case relies on outdated information and that crucial information was cynically hidden from view.”

Transport Minister Theresa Villiers has said: "Productive use of travel time is a complex issue and we have reservations about this study because it only provides partial analysis.

"We have taken the best approach to calculating HS2's benefits and our analysis is robust.”

She repeated the Government's stance that HS2 will deliver jobs, bridge the north-south divide and aid the rail network's struggling capacity.