Transport officials have shown "poor commercial acumen" in the management of the government's road-building programme, a Commons committee has said.

A report from the public accounts committee said that cost overruns on new roads were only being managed by putting back completion dates.

Committee chairman Edward Leigh said governments had been building new roads "since the dawn of civilisation".

But he said that the Highways Agency "is apparently unable to get on top of providing accurate estimates".

"As the costs of schemes soar, the agency keeps within its budget by delivering the schemes late, sometimes years down the line," he added.

"A lot of this is down to poor commercial acumen by the Department for Transport and the agency.

"On the basis of detailed analysis of the market - in particular, of the costs of construction materials and labour - they must develop strategies for keeping costs down.

"The agency must also develop much more sophisticated ways of judging whether enough progress has been made on a road scheme for the money spent."

The Highways Agency was also criticised for being too reliant on external consultants for project management expertise.

Leigh said the body must "recruit and retain its own staff with commercial skills and the ability to act as intelligent and challenging customers of the consultants".