Looking forward to your Megane impressions, Exonian.
Just thought I'd update my latest findings: This past week or so has been the first cold, Winter conditions for the Mini. Today's usual run to town and back along suburban roads in 5-7c and light showers yielded a battery consumption figure of 12%, compared to the usual 10% in warmer weather. Heating was set at 23c and the seat heaters for half the journey. So by my (admittedly primitive) deduction that's ~20% more energy used.
Now the interesting part (to me) is that the Mini has a heat pump, which from what I've read uses only 25% or so of the energy an element heater would use. So if anyone living there in the UK is considering purchasing an EV without a heat pump, be aware that Winter range may be significantly lower than quoted by the manufacturer, and achieved in warmer weather.
And to compound the issue, it seems most manufacturers don't list the type of heating in their specs, from what I've seen. I'd guess omitting the heat pump is a big manufacturing cost saving and one which a lot of buyers would be clueless about. So best to ask....