As a Brit I think it's caused by the success of Britain's foreign diplomacy and "image" projection reflecting back on the domestic population. The UK gets away with some pretty nasty shit abroad and has done for centuries but is rarely pulled up on it in the same way Russia, China or the US is.

Surprise, the UK also gets away with some pretty nasty shit at home too and is rarely pulled up on it.

For an illustration, you only need to watch Boris Johnson's speech at the Conservative party conference earlier this week where he says the world trusts Britain more than Russia, China and the US (see about 16m10s in here: https://www.youtube.com/watch?v=7NUPuArLSNs).

Whether that's true or not is debatable (I personally think the UK's game is up and any residual "free pass" given by other states/peoples is more due to our growing irrelevance than anything else) but it illustrates how the establishment (and by extension the populace) views itself.

Given the above, it's not surprising that most Brits would never stop to think how totalitarian their country has become. "That's something that happens in other countries, not ours!"

One could say the same about the US, but there are large groups of resistance in both countries. The mainstream media doesn’t always cover it. The UK Labour Party is the largest and most radical party in Europe for instance. And there are many protests all over the US.

It's most likely because 99.9% of Britons do not experience anything they feel particularly oppressive or totalitarian in their daily lives. Or rather nothing noteworthy or above the level experienced by most of the rest of the civilised World.

How do you get these people to concern themselves with the 0.1% of people who do have these experiences? That is a question which no Western country has answered, not just the UK.

It used to be more mono-cultural so standards used to be relatively more universal among the population and one authority would be less controversial.