7 to 21 days
Why so wide a time scale? Well, it is a long way from one end of the UK to the other (874 miles or 1,407 km according to the sign) and those doing the cycling vary greatly in strength, fitness and purpose. There is no set route and everyone will pick a way that suits them, so the distance will also vary. I have cycled several different routes ranging from 880 miles to around 1000. If you are riding as a challenge you might want to pile the miles in each day, riding dawn till dusk, but if you are touring you might prefer to meander and take in the sights at a more leisurely pace.
The record is less than 2 days! and many people take a few weeks. But the average is around 7-14 days – a week or two’s holiday with a day for travel each end.