[voidUpdate]

And in a situation where that is warranted (e.g. a traffic violation), you should probably have some form of proof of identification on you anyway

[stevekemp]

In the UK you do not have to have your drivers license upon your person when driving a car. Usually you'll be instructed to present it to a nearby police station within a few days.

[octo888]

Not required by law in the UK to have ID on you while driving. Works well enough (you have to produce it at a station within 7 days). I'm sure if it's serious enough, the police can force some other method

[michaelt]

In the UK all cars have number plates front and rear, so that's covered already.

[voidUpdate]

That gives the car's identity though, not the driver's identity