Rick asked:
I wonder how many Brits have a back-up source of heat (old coal burners?), or even proper insulation.
Very few modern homes have a back-up source, let alone a working chimney and 'clean air' regulations restrict smoke emissions in virtually all urban areas.

Insulation is another matter, although the government has repeatedly had campaigns to get home insulation improved - the last was free for all, rather than those on public benefits. Most modern homes are reasonably insulated, notably double glazing and doors. Cavity wall insulation is not standard and attic / roof insulation is haphazard.