In reply to CVaughanUK:
Yes Portland is definitely your best bet on the south coast. There's good variety on Portland, with thousands of problems on low ball boulders in the cuttings boulderfield, and other areas like the cliffs around Portland Bill offering some higher problems and areas with a high density of problems on vertical terrain. If you want to venture further afield there's Dartmoor but the rock is very sharp for newbies (I know, Dartmoor was my first outdoor bouldering experience!) and if you're going that far from London you might as well go to the Peak.
It's worth keeping an eye on the weather, if it's raining in Dorset it might be dry in the Peak District...