It's the dead of night and you're asleep upstairs.

The car outside is locked, the doors and windows are locked and you should be safe in your beds.

But downstairs, unseen and unheard, thieves could be at work, rifling through your personal belongings, taking what they can carry and then driving away - in your car.

The latest spate of thefts to hit Bromsgrove has highlighted a new target for the professional thief.

Instead of stealing the keys and picking off high-performance, status symbol cars, they're after anything that drives.

In recent break-ins in the Millfields Road, Brook Road and Dovecote Road area of Bromsgrove, they took the keys to a Vauxhall Astra, Peugeot 206 and a Volvo 580.

"We've known about these kinds of thefts for a couple of years and we've been running Operation Bandanna to tackle them," said Jo Hammond, of West Mercia police.

"At first, the thieves just went for cars like Audis and Jaguars. But now the offences have spread and they're taking the keys to any kind of car.

"Sometimes, they will use it to carry away other goods they've picked up while they've been in the house."

Thieves have been known to hook keys through letterboxes from stairs or hall tables. More often, they break into the house and take the keys, which are often left lying around somewhere downstairs or in a handbag, perhaps on the stairs or in the kitchen.

Analysts at West Mercia have been looking at patterns in the latest trend to draw up profiles of those involved.

"Manufacturers have made it harder for cars to be broken into by using security codes, so the thieves know they need the keys to get in," said Jo Hammond.

"They would now rather break into a house just to get the keys because they need them to get the car, whatever kind it is. Anyone can be vulnerable. There's always a market for selling on cars."

Police suspect many of the burglaries are the work of professional gangs from other parts of the West Midlands, or from as far away as Liverpool or London.

Bromsgrove's easy motorway access and affluent reputation could make it a target. In previous warnings, police have sent letters to residents in Oakalls warning them to watch out.

"New housing estates are targeted because they are more likely to have DVDs and computers and they're closer to road links," Jo Hammond said. "The thieves take the car, they're straight onto a dual carriageway and onto the motorway."

Police said they had stepped up patrols in the Millfields Road area in the last two weeks but burglary victim Paul Draper has already suffered.

While he and his wife Alison and her 15-year-old son Luke were asleep upstairs, thieves broke in through a front window and searched his downstairs rooms.

He had his personal belongings, including his birth certificate, driving licence and passport stolen, along with his DVD, video and stereo before the thieves made off in his firm's Vauxhall Astra. "It's a nightmare trying to get everything cancelled and replaced. I had to have the locks changed. They tried to use my credit card for a sale of £1,100 but I blocked it in time," said the 39-year-old security guard.

Police advice is to make sure you keep all doors and windows locked, even if you're just out in the back garden. In the summer, leaving them open can be tempting. They also suggest fitting security lights, taking keys and handbags upstairs at night and making sure the front of the property is kept visible by keeping hedges low. Putting the car away in the garage is also a good tip.

"It is worth being aware of security. Having thieves break in and your car keys stolen can just take seconds," Jo Hammond said. "But it can take a long time to get over it."