@VeloVixen (love your username) it's a terrace house, with solid walls, built in 1930.
We wanted to do a renovation on it, but wanted to get the heat pump installed while we could get the RHI, so we got it before adding any insulation, and actually because of lack of organisation have only just got around to putting insulation in.
When we had the gas combi boiler, the house was on the chilly side unless we had the heating on constantly - which would've been crazy expensive, so we wore jumpers a lot. Then we got the heat pump, and I was geared up for living in an ice box hell until we insulated, but actually, to my surprise, it was the same. The house is on the chilly side unless we have the heating on constantly - so we still wear jumpers a lot to save energy and money. 😂
Just in the last couple of months we've replaced windows and doors, put external wall insulation on the back and started on internal wall insulation on the rooms to the front. We're also planning underfloor insulation. I'm hoping this'll make a big difference in the Winter - it's certainly made things a lot more quiet, and cooler in the hot weather.
Honestly, I think that regardless of heating method, everyone should be able to insulate their house as much as possible given age and conservation considerations. And I think there should be easily accessible financial and practical help to do this - could the government back zero-interest upgrade mortgages, or train more insulation experts say? It's not fair to expect most of the country to struggle along in homes that are expensive to run and cold - people are literally dying at winter time, and most of the UK doesn't even get very cold.
Long-term, as the cost of heat pump installation reduces, I think that they will become a viable option for homes that really can't be insulated. The National Trust has even started putting it into some of their historic buildings. It's just you need a very powerful installation to overcome the inevitable heat loss, which is prohibitively expensive.
Also, there are other efficient electric options out there that aren't heat pumps, for example solar water heating, electric boilers, heat batteries and infra-red radiators, and these might be far more suitable options for some people.