I took the door card off on Saturday, following the instructions I have been directed to.
But under the door card there is an inner metal panel which keeps the window mechanism hidden. (This may not surprise anyone here but remember that I am a novice when it comes to taking things to pieces and I didn't really know what to expect to see). There are some spy holes in this metal panel, covered with stuck-on black material. I peeled one of these off and think I located the reset button. So then I reset the window, having printed off those instructions too. I wasn't brave enough to take off the inner metal panel and spray my new can of electrical contact cleaner about, not least because there were so many bundles of wires protruding. Feeling that I had already gone far enough outside my comfort zone, I put the door card back, which took a certain amount of effort/swearing. The window then worked properly for the rest of Saturday. Sniffing triumph in the air, I went to open the driver's door on Sunday morning but it started playing up again. So I am now getting in and out via the passenger door, it being impossible to close the door properly if the glass won't shunt down in time. Not very dignified.
I think I had better find an independent garage/auto electrician to look at it and maybe fit a whole new window mechanism.