Um, I should have elaborated in my original post - it most definitely is still heavily used in the UK by, for example, architects when evaluating how much heating a house will need. My original post wasn't terribly clear about that, my bad... Yes, consumer-facing information these days is indeed more likely to be expressed in kilowatt-hours...

I built a BTU-measuring device for a british customer, and he explained they had been using the metric system since the 70's.