Well, have spoken to his vet, and loads of the other ons too, I was on at the busy hospital surgery last night. Basically, they think castration is appropriate, so I can book him in there and get him done.
He's going to have a blood count, clotting factor test, and pre anaesthetic bloods done before they do him, on the same day. If there's any problems with any of the results we'll need to think again, but looks like Hamish will be a Jaffa shortly.
Thanks for all the opinions.