It's just that I prefer not to cut the power completely when "off". I
don't want it getting too cold (i.e. below 10C), even when I'm not
there.

If your house normally drops from say 20C in the morning to 10C by the
evening, I'd say you desperately need the insulation sorted.

Nah, it doesn't. In fact, despite lack of wall insulation, it doesn't drop
that much during the day. However, during the night, it could well go below
10C. Wall insulation isn't practical. It has solid walls and original
features that would get seriously disturbed. However, as it is a terraced
house, the overall heat loss really isn't that bad in practical terms.

Christian.