Car thieves are becoming burglars to steal car keys from houses in order to grab targeted cars, according to stolen vehicle recovery specialist Tracker.

The firm's managing director, Kevin Watters, said Tracker's stolen vehicle recovery system had logged 151 thefts of cars with keys since January 2001, compared with a total of 560 over the past eight years.

Of the 151 cases, 65 sets of keys were stolen from the car owner's house during a burglary and 35 were taken from the driver by force.

Watters said the rise was due to the increased use of immobilisers.

"Every car comes with one and they've got better and better but, if a thief has the keys, he's away to the races," he said.

"We've been doing this for eight years and in the first three or four, I don't remember a theft where the thief burgled the house to get the keys."

Over the past month, Tracker has recovered 25 cars stolen with their keys, nine of which involved the theft of the keys in a burglary and six involving the theft of the keys with violence.

This includes the recovery of a BMW Z3, which Tracker retrieved in 30 minutes, after its keys had been stolen in a burglary.

Watters said thieves were using some ingenious methods to obtain keys to cars they had targeted.

"People are being carjacked," he said.

Other cars were stolen at knife and gunpoint and one car owner was clubbed over the head during a burglary to obtain the keys.