Almost two-thirds of car seats leave motorists vulnerable to painful whiplash injuries in accidents, according to research published yesterday.

The tests showed 60% were inadequate in a rear-end shunt - the most common accident in the UK.

Among the cars given a poor rating were the BMW 3 series, the Jaguar X-type, Honda's CRV, the Toyota Corolla and the Renault Clio. Other poor performers included the Citroen C2/C3, Mercedes C-Class, Honda Jazz, Land Rover Freelander and Volkswagen Polo.

As many as 25 models automatically failed the examination because their positioning did not provide the minimum protection and they were therefore not tested.

Of the 114 models tested by the Thatcham research centre in Berkshire, only 18 were rated as good and a further 27 were just acceptable. The remaining vehicles were either marginal or poor.

In whiplash injuries, soft tissue in the neck is damaged by the sudden whip-like movement of the head. Of the 250,000 cases every year, 10% result in long-term symptoms and 1% of victims suffer permanent pain and discomfort.

Whiplash also places a huge burden on the National Health Service and adds an estimated £1bn a year to insurance premiums.

Women are more at risk than men from whiplash, and taller women aged 20-50 are the most vulnerable, with a 2 times greater likelihood of injury than their male counterparts.

Matthew Avery, head of the test programme at the Thatcham research centre, said: "These results are very disturbing.

"Some manufacturers - and motorists - will be shocked by these findings. Some models were thought to offer proper protection but, when we put them to the test, on our dynamic sled, the seats did not perform as expected."

He said the internationally recognised protocol for car seats was extremely accurate. "They have shown that seat geometry alone is insufficient to truly assess the ability of a seat to cope and protect in an accident. In a real-life accident, this could result in lasting, painful injuries."

He said manufacturers were certain to be embarrassed by the findings and would have to make significant changes if they wished to really protect people in car accidents.

Nigel Wonnacott, a spokesman for the Society of Motor Manufacturers and Traders, said: "The inference that we put unsafe seats in cars is nonsense. We know that whiplash is a concern, particularly for the insurance industry, but the reality is that four out of five whiplash injuries could be prevented simply by adjusting the head restraint properly."