By Louise Greenwood
BBC Radio 4's Money Box
The insurer was worried about the kind of cars that were being driven
There is growing concern that the number of uninsured motorists on the roads may increase after the UK's biggest car insurer said it is changing the level of cover it provides.
Norwich Union, which insures one car in every seven, is removing the provision called "driving other cars" (DOC) that allows motorists to drive cars belonging to other people if they have the owner's permission.
It says the clause is abused, enabling drivers to buy cover for a small car and then use high performance vehicles belonging to friends and family that they would not normally be able to get insurance for.
But others in the industry say the change could lead to more uninsured drivers on the road because people will continue to use vehicles they do not own, either because they have to, or because they do not understand the change.
Norwich Union's Head of Underwriting, Lawrence Loughnane, told BBC Radio 4's Money Box it was acting partly on feedback from the police.
"When they try to enforce the issue of uninsured driving, time and time again [DOC] makes it virtually impossible for them to do anything at the roadside," he said.
However, Peter Staddon, Head of Technical Services at the British Insurance Brokers' Association (Biba), said the move could backfire.
"I can see a lot more people on the road driving unintentionally uninsured...
"Some people will have [insurance] and some people won't. There will be huge confusion," he said.
Insurers Cornhill and More Than told the programme they are renewing their policies in light of Norwich Union's decision.
But Direct Line, Privilege, Churchill, Tesco and Esure say they will keep DOC.
Esure spokesman Adrian Webb said honest customers need it.
"There are scenarios where people have to drive other people's cars with their permission," he said.
"Often when someone is taken ill, say at two in the morning, you can't phone your insurance company.
"They would be taking to the road uninsured without it."
Norwich Union admits the move will save money but said it will be passed on to customers in reduced premiums.
The change will affect everyone applying for a new policy or renewing an old one with Norwich Union Direct from the New Year.
However it only affects motorists buying direct, not going through a broker.
BBC Radio 4's Money Box was broadcast on Saturday, 15 October, 2005, at 1204 BST.
The programme was repeated on Sunday, 16 October, 2005, at 2102 BST.