If you mean Fatsia Japonica ( the false castor oil plant ) then yes it can be pruned . They are normally pretty tough plants and unless you are very harsh with your pruning it should come back quite quickly. Mine gets so big I normally give it a light trim to keep it in shape.

If you mean Ricinus ( castor oil plant ) then I am not sure.

I imagine that it would be a wonder for a Castor Bean plant (Ricinus) to survive the winter in the UK.