From MOTOR LAWYERS Site
Do I have to carry my Licence at all times when driving?
Do I have to carry my licence with me at all times when driving/riding?
No, but it is strongly recommended. The Police are entitled to ask to see your licence at any time and if you do not have it immediately, you will be ordered to produce it to a Police Station within 7 days. Failing to produce within that period of time is another offence, even if you do actually hold a licence.