Motorists who travel abroad should check that their insurance extends to comprehensive cover, according to the AA.
The AA said that all UK car insurance policies gave drivers basic third party cover in Europe, but many comprehensive policies did not have this cover free.
One in four insurers charged a top-up fee, typically of about £30, for a fortnight-long trip.
An estimated four million UK motorists take their cars abroad each year.
AA Insurance Services managing director Andrew Briscoe said: "Motorists are too easily lured into the trap of focusing just on the price of their insurance.
"Unfortunately they find out the hard way when it comes to the crunch that not all policies are the same."