Fascinating and useful explanation. I think, then, the difference compared to the US must be that in the US, the majority of both parties have authoritarian tendencies, but there is a vocal minority of "libertarians" in both parties, whereas in the UK, you seem to be saying that libertarian pressure comes mostly from the outside the traditional political structure.
I do wonder, more broadly, whether it is possible for a country to have the benefits of the "European" approach (better social services) and of the "American" approach (more robust civil liberty) all in one, or if they are somehow mutually exclusive.
From the standpoint of security, I don't see much of a correlation between the level of surveillance/repression/etc and the level of terrorist activity. It seems to me the biggest determinants of whether a country will suffer terrorist attacks are: 1) immigration policy, 2) perceived level of "colonialist"/"globalist" behavior, and 3) wealth. It is very interesting to me that Poland has virtually no terrorist attacks whereas their neighbors, Germany, France, and UK, have them quite regularly, but I don't know the explanation. It is surely not that Poland regulates the internet more tightly.