Hi waterbuffalofarmer,
Many thanks for your advice. I'd feel dishonest suggesting he's suitable ram material as I'm pretty sure his wethering was just highly unsuccessful.
He's, very unfortunately, what seems to be a typical 'rig' (testes present but unable to descend properly).
His behaviour has become much more tup-like just recently, and he's definitely eyeing up the girls - even bothering the equine he shares a field with.
I think ending up in someone's freezer is, however sadly, the likeliest option.