The practice of charging motorists who take lengthy stops at motorway service stations to catch up on sleep has been condemned by an MP and a road safety charity.

Monmouth MP David Davies and the Institute of Advanced Motorists (IAM) have both criticised the actions of private firms who charge drivers who stop at service stations for longer than two hours.

Mr Davies, a former long-haul lorry driver, said the current two-hour limit on free parking should be extended and is joining the IAM to lobby the government to act on the issue.

He remarked: "Charging large amounts of money to park could be increasing the risk of accidents caused by driver fatigue.

"This is profiteering plain and simple. There is no justification whatsoever for making a charge.

"It is bad enough that motorists pay over the odds to buy a coffee or snack at a service station without the worry of paying vast charges for taking forty winks."

He concluded that the policy of charging motorists for longer stays is "contrary" to their primary purpose of giving drivers a place to stop and rest on long journeys.

Similarly, IAM director of policy and research Neil Greig said drivers may worry that they will "inadvertently" overstay their free period and accused service stations of being more interested in selling expensive food and goods than of helping motorists get the rest they need.

The IAM has pointed to the Department of Transport's own data to show the dangers that tired driving can cause.

Data from the department's THINK! campaign has shown around a fifth of accidents on major roads are due to drivers being short of sleep or nodding off at the wheel. Moreover, these accidents are more likely than other kinds to result in death or serious injury.

The charity has included the call for an extended period of free parking at service stations in its own manifesto, which it aims to highlight as the general election approaches.