Thanks Emaggie, we usually walk in the woods at home which is very soft on his paws, so you are probably right we do need to toughen him up a bit! We have started to pound the pavements some more. Dog friendly beaches are usually the most gritty -he loves swimming and the beach though, so it wouldn't be fair to ban him from the beach alltogether!
We found some wax in the pet shop the other day which you smear onto clean paws and it is supposed to help with scuffing and sea salt etc, we will try it out before going on holiday as I am not convinced that grit will just stick to the wax.