Soaking, vice and hack saw - all ultimately unsuccessful. I think I was too impatient with the hack saw and didn’t cut far down enough, because I managed to fold it in but it’s still stuck further down the seat tube. I haven’t touched it for a few months but told myself I’d give the caustic soda method a go over the summer. I’m attracted to the ‘slow and steady’ method that
@Ray_72 describes as it sounds like it gives me the best possible chance of preserving the paintwork, which is basically pristine!