Car thieves are making a mockery of sophisticated alarm systems on high performance vehicles by breaking into the owner's house and stealing the ignition keys.

In the last two months alone, Bradford's Eccleshill Police division has dealt with 30 burglaries where cars have been stolen from the scene.

As manufacturers place more emphasis on safeguards to protect expensive cars, thieves are realising they can no longer rely on traditional methods like "hot wiring".

Detective Inspector George Marshall, of Eccleshill CID, explained: "As modern cars are more security orientated, thieves are finding them more difficult to steal. Breaking into people's homes first means they can get the ignition keys. Expensive cars are being targeted."

The latest incident happened early today when a Mercedes and Mitsubishi Shogun, worth £60,000, were stolen from outside a house in Leeds Road, Idle, Bradford.

Businessman Dean Underwood woke to find the top-of-the-range cars missing from the garage and driveway of his detached home.

The 33-year-old, who runs his own computer business in Bradford, said: "They broke into the house and grabbed the keys to the cars and garage.

"They seemed to know exactly what they were looking for. It makes you wonder if they had been watching earlier in the day."

The break-in happened shortly after 3.15am today. The green and gold Mitsubishi, registration R839 BNH, and silver soft-top Mercedes 230 series, registration W166 OBD, have still not been recovered.

Mr Underwood said: "They're most probably in a lock-up somewhere, but they are distinctive cars and someone must have seen them.

"It's so frustrating when you work hard to build up a business and buy nice possessions, only to have them stolen."

Of the 30 cars stolen in the Eccleshill division since the beginning of August, 25 are still missing.

Detective Inspector Marshall said: "This type of offence is becoming more common. People should guard against it as much as possible by hiding their keys - not leaving them in the front door or on a kitchen worktop."

Anyone with information about the incident in Leeds Road, or the whereabouts of the two cars, should contact Eccleshill Police on Bradford 376085 or Crimestoppers on 0800 555 111.

l Two youths have been arrested in connection with the incident and were being questioned at Eccleshill Police Station today.