Electronic gadgets capable of hacking into a car's security systems are enabling thieves to steal thousands of cars with the minimum of effort.
Sky News reported that half of all car thefts in London last year were carried out without resorting to force, such as smashing a window or intimidating the owner.
Experts warned the problem is deepening, with 21,000 cars stolen in London last year. It means the trend could pick up after years of declining motor thefts.
Security specialist Mike Parris said stealing a modern car using a device originally intended for use by locksmiths is possible in only a matter of seconds.
The tool costs less than £25 and comprises an on-board diagnostics (ODB) bypass device, which is usually shipped in from China or eastern Europe.
All vehicles are vulnerable to these devices, which are relatively cheap to buy, easy to use and for sale on websites.
"It is getting worse," Parris said. "The tools are becoming much more readily available. The price of them is falling. And they're operating much more quickly - you can re-programme a key in a matter of seconds.
"All vehicle manufacturers are aware of the problem. It's fair to say some are doing more than others.
"Car manufacturers are acutely aware of the need to constantly make their vehicles more secure because they know criminals will adapt and develop."
Theft is not the only potential problem for owners of modern cars, which each rely on around 50 low-power computers. They could suddenly find it is impossible to control the vehicle which they are driving.
Recent cases of high-tech car hacking saw computer geeks disable the brakes on a Toyota Prius so that when the driver pressed down on the pedal, nothing happened. They even hacked into the steering wheel, enabling them to take control, and also honked the horn at will.
Meanwhile, the very high-tech Tesla Model S is vulnerable to basic basic hacking techniques which can be carried out on an iPhone, warned one expert.
Niotesh Dhanjani told a conference the car's computer system could be unlocked by simply getting the right password in a matter of seconds.
A Scotland Yard spokesman told Sky News: "Vehicles are becoming more technologically advanced and the criminals are becoming more savvy towards that technology and they will develop."