Thanks for all the advice folks. I would take it to Jonathon at Feline if I was more local, but it's a bit of a trek unfortunately :(
I've just spoken to my local luthier on the phone and he's suggested the heat and clamp treatment, which he has done before. I've used him for other (more minor) work in the past and he's done an excellent job so I feel I can trust him with this. He says a full setup and neck treatment is going to cost me about £90 so I'm going to give that a go. I really hope he can save the original neck as it's so superb to play.
Fingers crossed....