Have a look down the gap at the top of the lock looking down at the barrel so you are looking at the side of it (inside the lock handle mechanism) you will see a little brass nipple that needs pressing in. Once done it will remove on your key.
Cheers, lads. Amazingly, it was not seized! The pin compressed easily and the barrel just slid out. I put the barrel in penetrating oil over night. I'll see tomorrow if it fits new handle/mechanism.
There you go Terry, though it's not the most exciting picture. It's blurry too
The penetrating oil must have worked on the tumblers, because they tapped loose reasonably easily. Worked them back and forth with a screwdriver and some oil , so they would spring in and out with the key.