It's a big place, the north is essentially a cooling year round climate.
Most of the older places have very little insulation, lots of airflow, single pane leaky windows.
Usually the areas you need to fix are air leakage, better windows (double glazing), then in ceiling insulation. In order of impact.
Our construction industry is pretty much broken, and considers double glazing advanced luxury alien technology... So it can cost so much to replace the old windows that you can run heat pumps as much as you like with the interest on the sum.
And without that the improvement from more diy insulation upgrades don't really achieve much in a monetary sense.
On the other side, we have a much better solar and battery uptake, and the cost to install is fair. So a typical house might be a leaky wooden crate, but with enough solar and battery to be comfortable anyway.