> Subjectively, most UK cities feel less dense than many continental cities, with less apartment living and more urban streets with two story terraced houses

I suspect this depends upon the part(s) of the UK that you visit. If you were in Glasgow, or Edinburgh, up in Scotland you'd find that the majority of people live in tenements:

https://en.wikipedia.org/wiki/Tenement

There are huge swathes of the country where people live in terraced homes, and still more where people have detached/semi-detached. I suspect if you wandered around in London you'd find both of those, as well as the ubiquitous tower-blocks.