User error - Caygill broken!

I think you are right Dylan - thanks for the advice. Wheres BoB the Builder when you need him?
Cheers jonny, perhaps I can just zip-tie the saddle to the frame? ;-)
Since it's summer I will put it aside and dig it out when the sun is gone and I have the ££s. It may even enjoy a return to Arthur caygill himself! He only started putting his name on bikes in 1989, and 753 is pretty archaic. so it may well be an early frame for him and a nostalgic repair?
if I get it repaired it may still end up too small for me though! BoBoB has first dibs.

good luck with repairing it, it 'll be fun getting involved in intensive bike frame surgery.

make sure you have oxygen and adrenalin ready if the worst comes :)