A public spending watchdog on Monday said the Department of Transport had failed to present a "convincing strategic case" for the controversial ??50 billion HS2 high-speed rail project.

The Commons public accounts committee said the projected economic benefits of the link were based on "fragile numbers, out-of-date data and assumptions which do not reflect real life."

It also dismissed as unfounded claims that it would boost regional economies and encourage investment outside of London.

"The Department has yet to demonstrate that this is the best way to spend ??50 billion on rail investment in these constrained times," said committee MPs.

They warned there was insufficient evidence "that the improved connectivity between London and regional cities will enhance growth and activity in the regions rather than sucking more activity into London".

Transport Secretary Patrick McLoughlin dismissed the findings.

"The project will free up vital space on our railways for passengers and freight, generate hundreds of thousands of jobs and deliver better connections between our towns and cities," he said.

"HS2 is a vital part of our plan to give Britain the transport infrastructure it needs to compete."

The first phase of the plan, a link between London and Birmingham, is due to open in 2026 with an extension to Leeds and Manchester set to be up and running by 2033.