dunno if you meant in s.a., or in the UK, but my wife got stopped on monday, and was given a form to fill in, and take to the police station within 14 days to show her license and insurance etc.
so, no, in the UK it is not compulsary to carry driver's license with you at all times. In fact, besides my car keys I normally have f*all on me at any stage of the game, barring a few £££'s in my pocket.
and as we have no id cards or books here, guess you can be free to walk around. just be aware of the cameras following you...doo dee doo dee doo dee doo dee doooooooooo
Meant in SA, my brother got a R100 fine a while ago for not having his on him at the time.