Post wrap-up (from my POV)
After some digging and the recommendations above, I found a few insurance policies covering theft after leaving a bike longer than 12 hours. Listing in case they are helpful to others:
- Laka (up to 24 hours; theft only)
- Bikmo (up to 24 hours; also covers public liability + personal injury)
- Cycleguard (as per Bikmo)
- Assetsure (as per Bikmo)
- TSB pick & protect (no time limit in their policy - I called them to check this; theft only)
My comparison was to ETA (covered for only up to 12 hours but also covers public liability + personal injury).
After looking into policies and comparing quotes I think I'll keep ETA and add TSB pick & protect. This is not the cheapest option but I want to maintain medical/accident insurance (should have mentioned this earlier, but tbh I completely forgot that this was a component I also valued) and I think not having a time cut-off will be helpful, especially for those of us who are not going to work all that often in the current circumstances.
This post generated lots of discussion on the usefulness of and alternatives to insurance; a lot of this was not relevant to my situation so I did not engage, but may be useful to others reading this thread. I agree insurance is not necessarily essential or indeed worthwhile, but it's something I decided was desirable for my situation. Frankly, I envy those on this thread who've never had bikes stolen! You're probably lucky or in a very different living situation to me (or both): in 5 years of hefty commuting & recreational cycling around large cities I've had 2 bikes stolen. Both were well locked but in the same place for more than 1 night in a row (I know, I've learned my lesson).
Naturally I do everything I can do minimise the risk of theft regardless of whether I have insurance or not, but right now having to replace the bike I have would be a big hit for me, hence my decision (and I recognise even taking insurance doesn't necessarily mean they'll pay out). I have also since emailed my local councillors about getting more bike lockers as this is clearly an equity issue (seems unfair that my bike is more likely to be stolen than someone across the road, just because they live in a fancy apartment block with secure cycle storage facilities and I can't even pay to access something like that). No response yet, but tbf that was over the Christmas-NY period so perhaps their offices are still closed.
General cycling advice ( NOT technical ! )
Thank you: I expect that summary to help a lot of us.