Had cavity wall insulation injected last year, I have to say I’ve not found any diffence to my heating costs or the temperature of the house.
I have a front entrance area which has always been freezing even with a c/h radiator in it, it still is now, the insulation has made no difference at all.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!