Huge range of efficiency difference between houses. (How did "Insulate Britain" fail so hard?)

I had an actual aunt called Mildred, and she lived in a very old (possibly literally Tudor, not mock, actual) cottage with actual fireplaces and so on.

Her place likely used about 42 MWh/year to heat, though this would be coal and wood not electricity because actual fireplace, compared to my house which is so well insulated that it took a week to notice we'd switched off the heating, in winter, while it was snowing outside.

For 42 MWh/year, you can fully recharge a 100 kWh car battery every day and still have more left over than my house consumes in total.