As shocking as this is, it's not _surprising_
I'm 55 and pretty well travelled and I've noted similar levels of coverage in many EU countries and the US and CA and of course CN (to be fair, my experience of CN is only HK).
I don't know why people get so whizzed up about London's CCTV coverage. For me the scariest area is the M42 south of Birmingham. Every few 100 yards there is a high level camera at height and lots of ANPR.
It is quite a logical place to concentrate on. Look at a map of England - Brum is in the middle of England and the main roads run nearby. M1 from the southeast, M5 from the southwest, then M1 and M6 (takes over from M5) carry on to the northeast and west.
My own house has six HD cameras with Frigate to co-ordinate, analyse and record. My Reolinks never get to see the internet! Four are on the garden and two watch the front door, one is the door bell.
Now ... "since the '70s": I'm old enough to remember the seventies (I still have several mugs for the Queen's Silver Jubilee in 1977, when I was seven). Back then video (VHS) was not a thing, neither was CCTV. We had three TV channels FFS! A cutting edge TV camera at the time was a huge beast and certainly was not mounted on a building or street lamp.
Are you a local?
Anyway, on the cameras you're spot on. I do wonder how much UK cameras are used though - like a microcosm of our national potential, the cameras have potential but how often are they really used: half are likely faulty, most have the person monitoring them on a tea break when something happens and it seems to need an extreme act of violence before they get used in earnest.