The door interlock didn't work any longer so we bought a new part and found a youchoob video that looked similar. Of course, when I got down to it I found I couldn't see what I was doing and the part, while correct and similar to the video one, was going to require more knowledge of the actual situation than I had.
So, repair chappie came this a.m., fitted the door part, still getting "door not interlocked" error code. He eventually diagnosed the power supply board and replaced that, all OK thereafter. Cost nearly £200, though, about 50% of the new price. Seems a bit steep.