It's been a month, though very little sun and very low when it is out so I did another check. Presumably the worst time for solar panels until we're well into February.

Voltage on the battery was below 12V but it did start quickly despite turnover being a bit sluggish.
Left it running for quite a while to get thoroughly warmed up and blow some dry air through the cabin.

It's been a while and it's been on SORN for over 6 months now, with the big AA solar panel plugged in.
That seems to look after the battery to some extent, but not completely, enough to keep the basic electrics (locking, radio codes etc.) alive for sure over winter.

I have connected an external charger just once in those 6 months and run the engine 2 or 3 times, more to blow its cobwebs out than for the battery.
To be honest I'm not sure the battery is in tip-top condition despite being relatively new. I think it's a Halfords/Yuasa that others have had issues with.

Today I have connected a charger again just to make sure the battery is back up to starting power. It's my birthday this weekend so I might just have a little run round the block.....