@slh @FloatingBoater thanks so much for taking the time to guide me on - not complaining - a much more complex quest than I realised!
I can narrow my wish list down quite a bit though:
- ZigBee: because l already have a SONOFF ZigBee dongle and a couple of SONOFF temperature and humidity sensors or..
- ESPHome: where I want more capabilities (such as built in Metering and device based automations)
- No Cloud: for independence and privacy
- HA App: I don't mind dependence on HA for control atm, BUT...
- Metering in Plug: I would like power monitoring to include sampling in the plug rather than just being calculated in HA using polled values
- Reliability: going for 16A sounds wise, but not essential at this point as I'm learning rather than implementing something specific, but it is BS certification that really matters
- Cost: I'm only starting small so not too price sensitive yet
I hadn't even come across Tuya before you mentioned it! So much to learn 
I'll do some searching based on the above but if anyone knows of a UK plug meeting the above please share.
I think in plug metering might be the tricky thing for me to check, assuming it's available!?