There is probably a legitimate basis for some powers against actual foreign intelligence operations. But the proposals in the article defining "subversion" to include environmental activism, independence movements, or criticism of UK policy show how quickly these things expand beyond their original scope. The Terrorism Act was meant to exclude domestic activists but two decades later it has been used against protest…
It will never cease being funny to me how Eurocrats/Anglocrats pout their chests, proclaim proudly how "free" and "democratic" they are, and then proceed to implement a police state and surveillance regime which the DDR could only dream of. Sure you have "nothing to hide", and "intentions are good". Was that also true for every decade in European history? Will that also be true in 10 years? In 20 years?
That's weird, I've never met a single one since we don't even have a constitution to enshrine civil liberties.