Hmmm, maybe. They will shed at this time of year anyway, I'm in the South East too, being in Essex. Nigel shed his baby fur and started to look a little odd, like his fur was in 'steps'. he ended up with a kind of saddle shape as it shed in stages, with the more coarse fur coming through. Just keep grooming him I guess.
As for the food, I can't say really as I have 3 of different ages and fed them all the same stuff. Excel do a junior and dwarf pellet, which seems to suggest it's suitable for adults too, so it can't hurt to keep on with the junior for a little while longer.