New build does have fairly high insulation requirements, hence the abilty to heat a normal house with -10C outside with a tiddly 10kW boiler... But there is an awful lot of "old stock", that leak heat like a seive, think of the 30's estates with double solid brick walls or older stone built places. You can insulate those either with 50mm of celotex/kingspan inside (loosing at 3" off the room dimensions) or outside cladding but niether are quick or cheap to do, hence there are no grants or aid to do it.
At least no grants or aid that I know of, if there is I'd really like to know as internal lining is what is about to happen to this 300 year old building.
I like that word.