Believe it or not, after trying the shaft from a pop rivet, (strong, smooth and exactly the right thickness), with a lucky shake the cylinder finally came out. Only took nearly a week!
Trying it our on the bench after removing it, it was clear that the catch was not moving very far, and whatever I was trying in the hole wasn't hitting the right spot. But never mind, it's out.
Right, so now it's a question of what is actually wrong, as you can see from the key and cylinder video, they are not jamming at all. Looks like the cylinder is jamming at the steering lock point I think, unless it's the ignition switch at the far end. I might try and remove that next before taking out the barrel.
Stop Press : ignore comment about video as the file size is too large.