Isn’t most of the housing in the UK from the 1970’s too?

No. The majority of it, still, was built before 1920.

(The ground floor of my house, which is, to be fair, quite damp, was built 220 years ago; this is not all that remarkable and my neighbours' houses are fifty years older)

1970s houses are pretty energy-efficient by comparison.

But it's worth noting that a surviving 100 year old house in the UK is likely to be warmer than a surviving 100 year old house in the USA; it is not only brick-built but it is also likely to be in a terrace of several houses, so it has some of the heat retention advantage of an apartment.

The "newer" town in my area is a railway town — it is actually a very old settlement but it became a big important town when the railway arrived in the early 1840s. Much of the housing in that town dates back to the 1860s through to the Edwardian era at the latest and is small houses in brick terraces of ten or fifteen houses in a row (usually in staggered terraces of four or five).

These houses are all supplied with natural gas now, and they have increasingly well-insulated roofs (and loft conversion rooms), double and triple glazing, so they have become warmer and pretty energy efficient.

But in the early 1970s, many of them still would not have been on the town gas supply, they would have been burning a lot more coal, and therefore almost all their supplemental heating (cooking, much of their hot water) would have been electric.

About half the homes I've lived in (maybe a dozen?) were built before WW1. Lots of Victorian conversions.

My house is from the 1870s.

No? It would be pretty remarkable if the majority of all UK housing was built in a single decade. If you meant to say 'from before the 1970s' then that might be a more defensible claim. But old houses can be upgraded with double glazing, insulation, etc.