As many as one in nine cars have defective or incorrectly adjusted headlights that can temporarily dazzle oncoming motorists.

During a survey by Norwich Union Risk Services (NURS) of 376 cars travelling on roads at night, more than 10% had headlights that impaired the visibility of oncoming motorists, and nearly 10% had their dipped headlights set so they appeared too bright for oncoming traffic.

Bill Pownall, Norwich Union's motor risk manager, said: "The problem appears to be mainly due to driver error, rather than defective equipment and none of the cases recorded involved drivers forgetting to switch off their high-beam when traffic was approaching."

Many cars feature headlights that can be manually adjusted to suit different load conditions.

"According to our research many drivers are failing to adjust these settings under certain circumstances, and as a result are dazzling other road users,” said Mr Pownall.