London is 2000 years old. There are lots of historic buildings. There are energy saving grants available. Building regulations on insulation (including glazing) are very strict, but they're not retroactive until further work is done on the building. That's when you do see the double glazed units in sash windows. These are, incidentally, very expensive items, but then so is most listed building work. If you don't want it, don't buy a listed building.