Parents should be advised to follow their Scandinavian counterparts and keep their children in rear-facing car seats for as long as possible, a British Medical Journal study warns today.

While it is common to switch babies in the UK to a forward-facing car seat once they weigh around 9kg, which on average is reached at eight months old, doctors Elizabeth Watson and Michael Monteiro argue in the report that it is safer for young children to travel in a rear-facing seat until they are at least four years old.

Although the idea might sound odd, rear-facing car seats for older children are widely available, and widely used, in countries such as Sweden, Norway, Finland and Denmark.

In the UK, the only legal requirement is that children under 12 - or less than 135cm (4'5'') tall - must use a car or booster seat; there are no recommendations about when to switch between front- or rear-facing car seats.

However, the authors say that, because rear-facing car seats keep the head, neck and spine fully aligned, the forces of a impact are evenly distributed across these areas of the body. This results in fewer serious or fatal neck injuries.

They highlight data from Sweden, which has shown that children who died in accidents restrained in forward-facing booster seats could have potentially survived if they had been travelling in rear-facing seats instead. Another study using the US crash database concluded that rear-facing seats were more effective than forward-facing seats in protecting children aged up to 23 months for all road accidents.

The BMJ paper echoes the findings of a report published 12 months ago by ANEC, the European consumer rights and standardisation body.

It argued that "a gulf has developed between the conclusions of the technical community, based on accident and test data, and advice provided to consumers through legislation", and urged manufacturers to make the rear- facing restraints for children aged one to four generally available in Europe, rather than just to Nordic consumers.

Helena Atkinson, from Southampton, has been running a website calling on retailers to start stocking the rear-facing car seats for the past 18 months, after hitting a brick wall in her quest to kit out her own daughter - then nine months old - with the European-style restraint.

"I couldn't believe it. The sales people were telling me that they knew about them and knew that they were safer, but they wouldn't stock them because no-one here wanted them. But no-one is going to ask for them if they don't know about them", said Ms Atkinson.

She urges parents to pester companies until they respond to demand.

Duncan Vernon, a road safety manager for the Royal Society for the Prevention of Accidents, also backs the advice. He said: "The evidence shows that it is safer for children to travel rearward-facing for as long as possible, although that does not mean forward-facing seats are dangerous'.

"For parents who currently have a child in a rearward-facing 0+ car seat and are wondering what to do next, our advice is to keep them in that seat until they reach the upper end of the weight range (13kg), unless they have grown out of the seat in terms of their height.

"Greater availability of rearward-facing seats in UK sales outlets is important, so parents do not order a potentially- misfitting seat over the internet before they have had a chance to seek expert guidance."

However, Halfords - one of the UK's leading car seat retailers - said they had decided against stocking the Scandanavian-style models because they were "difficult to fit".

A spokeswoman added: "While we agree that rear-facing car seats could offer improved safety performance, these types of seats are generally unsuitable for many of the cars driven in the UK.

"Rear-facing seats for infants are larger than front-facing seats and the tether straps are not long enough to fit all cars driven here in the UK. Rear-facing seats for infants can be complex to install, which could lead to unsafe fitting."