Many European countries have much high per capita rates than the U.K. You can see where we are on the list here
https://www.statista.com/statistics/...pe-by-country/
Back to traveling within the U.K using your logic. If we already have high levels throughout the U.K why the worry about families mixing at Christmas and why are the 4 nations saying think carefully? Maybe the clue is what happened after Thanksgiving.