You don't have to carry any form of ID in the UK and there are no ID cards, anyway. That said, obviously most people have their driving licence on them.

As a foreigner you do not have to carry your passport.

No-one is going to ask for ID unless you are doing something specific at a bank or government office, for instance. Or, indeed if you are trying to buy alcohol or cigarettes anywhere and look very young... But young people can get provisional driving licences before they have passed their driving tests.

> That said, obviously most people have their driving licence on them.

Just to point out for the wider audience: you're not legally obliged to have your driving licence on you either when driving. You have 7 days to produce it a police station

I wouldn't say you need to look very young. I've been asked to show my ID when entering venues and buying alcohol[1], and I'm nearly 30. I might look under 25 if you're being generous. As a result, I usually carry my passport.

[1] Well, zero-alcohol beer, which is considered alcohol for this purpose.