Thanks everyone,
As usual, some very helpful advice.
I have given the grubby wool on his back end and abdomen a good wash down with Dettol soution. Then dried it off with an old towel. Have put tea tree oil ointment on the rough skin on his chest. Didn't have a chance to look at his anus before it got dark, but will do so tomorrow. However, he was sitting down very determinedly this evening, so there might be a problem in that area. Unfortunately i don't have Battles maggot oil, so that isn't an option.
He didn't come to the feed bucket this evening, was looking rather sorry for himself and was still being bothered by flies. However, he did eat the sheep nuts when I put them in front of him.
Smallflockshearing - he is a suffolk down x norfolk horn so does have a thick fleece despite his young age. I have had a good rootle around in his fleece this evening and can't see any maggots so am hoping for he best.