Thanks Fleecewife, that's a really helpful reply!
I probably should have said in my first post that he's a pet and not intended for meat. He came from my brother-in-law; they don't live locally so I haven't been able to get his opinion yet, so thought I'd have a look at what I could find online!
His toes have always been a little bit separated but have got worse as he's grown. The back ones didn't curl around like they do now. This is how they were when he was smaller, not a great pic but the only one I can find showing his feet:

They don't seem to cause him any problems yet; he isn't lame and is happy to run around etc. Unfortunately all the farmers around here are arable, so there's noone else to look other than the vet, but if it's a malformation I'm not sure if they will be able to do anything other than say to have him killed if it begins to interfere

He's our only sheep; he lives with our horses for company and seems happy with this for now. We've considered getting another but it depends on his feet and how long he will be around!