Great news Welshkiwi.
I have been working my way through the fuse checks to see what is causing the draw. No progress during the cold snowy weather, and up to Fuse 31. They are fiddly little blighters, even with the extractor tool.
As I am using one of these:
there are two insertions and two extractions for each fuse. And due to the position of the fuses near the bulkhead, you tend to stand a bit too close and have to lean backwards.
However, now that the battery is charged up, the solar charger on the dashboard that IanA recommended seems to be doing the job. I have also bee taking the car out for a 10 mile trip every 5 or 6 days just to make sure that it starts and goes.
The fuel gauge warning beeps and the light comes on when ignition is switched on. Internet advice is to put some fuel cleaner in the tank a few times and see if it frees up the sensor mechanism. I had let the fuel get very low, so it is possible it is gunked up. We shall see. Otherwise it will be a sensor replacement.
The car drives noticeably but not unpleasantly firmer on the coil overs, so that is a relief. I really only got them to accommodate the wider wheels on the front and to allow height adjustment once the new panels are fitted. I got AP coil overs, and was advised by a mechanic (after purchase) that they are prone to knocking in the Z3 mounts. Luckily, that has not happened either.
Edit. Now checked fuses up to 46. The only draw is on the alarm / door lock remote circuit, so nothing is out of wack so far. I think there are some under the dashboard to try, and also there is a possibility of a sticky relay switch. I'll just have to keep plodding on.