In the UK you don't have to carry your license or insurance while driving - although you can be required to give your name, and to take those documents to a police station within 7 days. For certain crimes they can also arrest you and/or seize your vehicle.

Of course, in the UK car registration plates are issued and attached by the dealer, before a car's first sale, and they never expire. So they can find the registered keeper of a vehicle just by looking at the plates.