An epidemic of smash-and-grab incidents has made portable satellite navigation units the biggest threat to vehicle security.

After Christmas, when many car drivers were given the systems as presents, the number of thefts from cars leapt by nearly a fifth overnight.

Windscreen repair firm Autoglass was called out to vastly more smashed side window repairs in the first week of January than in the preceding years.

In total for the January to March period it has seen a rise of 17% over last year in the number of bodyglass repairs.

Nigel Doggett, managing director of Autoglass, said: "We’ve seen a significant increase in demand for vehicle bodyglass in the last year, which is indicative of the rise in smash-and-grab incidents across the UK.

"The large range of driver assistance and entertainment devices that are now in use, including satellite navigation units, digital media players, Blackberries and laptops, has proved fruitful for thieves who are willing to break side windows in order to steal such items."

Lesley Upham, director of communications at vehicle security expert Thatcham said: "Figures highlighting any sort of vehicle security trend are always a cause for concern for Thatcham and our member insurance companies.

"Thatcham’s advice is a common sense approach, removing the sat-nav cradle and display and keeping them out of sight in the glove box or boot.

"Longer term, we would like to see sat-nav manufacturers building security features in, such as unique PIN codes in order to make the system operable."