Timpsons didn't have a punch big enough (went down the middle of the pin), the jewellers spent 5 minutes pounding the crap out of it and got nowhere, and nowhere else had the tools....
I've found a small allen key from my bike multitool that fits, spent about half an hour hammering the hell out of the pin to no avail. Pliers can just about grip the protruding end but get no movement. I've soaked it in WD40 for half an hour to try and loosen it (only lubricant I had to hand) and no luck. I think it needs a vice and some brute force/ignorance! Hopefully get it sorted this weekend, off to the mrs' parents, her dad has a garage full of tools which should provide some progress...