Yes true but if you put the same amount of people into two acres it is far less dense than putting them into one acre for example.
Italy
Population: 60.36 million
Eurostat
Area: 301,338 km²
UK
Population: 66.65 million
Eurostat
Area: 242,495 km²
Spain
Population: 46.94 million
Eurostat
Area: 505,990 km²
So while both have smaller populations, Spain very significantly so, they both have a larger area to fit them into, Spain massively so.
London again can be compared to Rome and Madrid
London
Capital of England
Population: 8.982 million
Eurostat
Area: 1,572 km²
Madrid
Capital of Spain
Population: 6.642 million
Eurostat
Area: 604.3 km²
Rome
Capital of Italy
Population: 2.873 million
Istat
Area: 1,285 km²
As you can see London is huge in population terms and far more densley populated, being a smaller country it's far more commutable to the rest of the UK too. It's not surprising it was worst hit.
There's a marked call correlation between population density, and more so closeness of the most populous city to the rest of the country to the figures for both cases and fatalities.
It's why the countries that break that trend stand put more, South Korea and Germany on the positive side and Sweden on the negative.
The other countries more or less correspond to how you would predict. Unfortunately the UK is the most densley populated in Europe by a long way.