So, I unplugged it all and unscrweed the shaver adaptor, meaning to adjust the contacts with a handy pair of pliers (turned out one was bent out of shape). And I decided to get them out to make it easier to get at. This required removing the fuse.
Fuses in the UK have to conform to one of the various standards, which IIRC amongst other things requires them to be filled with sand and I think be in cermaic cases.
This does not mean in a glass tube with loose end caps, as it turned out this plug used. I seriously doubt that conforms to BS646. I now need to buy myself a new fuse, as I will not be using that. Those have a tendency to go with a bang.
Worst thing is is that I think that was an off-the-shelf plug, and that was the fuse it came with.