A campaign designed to encourage drivers not to use their mobile phones has been criticised as "misleading" by motorists' groups.

Both the Royal Automobile Club (RAC) and the Automobile Association (AA) say hands-free mobile phones are safe, while the government is keen to stop all phone conversations by drivers.

The government's campaign, with the slogan: "Stay switched on. Switch off", is based on TV ads which feature a short film - a montage of still photos from a reconstructed accident.

The sound of a police radio can be heard in the background as an officer reports an accident involving a pedestrian who was killed by a driver who was on the phone.

The campaign follows concern that the huge number of mobile phones in Britain - 24 million, with four million sold in the past three months alone - could pose a serious threat to road safety.

There are no official figures for accident or injury resulting from in-car phone calls, but there have been a number of fatal accidents where phones have been involved.

In 1997, the Transport Research Laboratory said one in 28 fatal road accidents involving distraction inside a motor vehicle involved a mobile phone.

The Royal Society for the Prevention of Accidents (Rospa) says six deaths on Britain's roads have been linked to the use of phones.

The government has ruled out new legislation to ban the use of phones in the car, saying a motorist could already be prosecuted for careless or dangerous driving.

Road safety minister Lord Whitty says drivers who want to make or receive calls should pull over.

He said: "Using a mobile phone when you're driving a car is stupid and can cause serious accidents to yourself and other people."

The campaign was welcomed by families of accident victims.

Robert and Valerie Hammond from Cresswell, Staffordshire, whose daughter Carole was killed after being hit by a lorry whose driver was replacing a handset, said drivers should never use phones while at the wheel.

Mr Hammond said: "They don't realise the dangers. If they saw the consequences that we did, they would stop and think."

Rospa said there was no need to use a mobile phone in a car.

"We would like companies to reinforce this campaign by making it part of their health and safety policies that employees should not use mobile phones while driving," it said.

But other bodies criticised the campaign for failing to make a distinction between hands-free and hands-on systems.

Motoring organisation the RAC said modern hands-free technology requires much less hand movement than putting on a tape, and no more distraction than talking to a passenger.

AA spokesman Adrian Ruck told BBC News Online: "Hands-free mobile phones are basically safe. They are no more distracting than listening to the radio.

"In an ideal world you would not use them but you can't just disinvent the mobile phone."

He said: "Drivers should be sensible. For many people nowadays their car is like a mobile office but if they know they have an important call to make they should park up before making it."

Mr Ruck said hand-held phones were an absolute menace and he added: "There is nothing more dangerous than trying to drive while balancing a phone on your shoulder and argue with your wife or plead with your boss. It is a recipe for disaster."