We already have warrants, judicial oversight and public audits to prevent abuse of power. Not sure what's authoritarian about standard overt surveillance.

No, not in the UK. XKEYSCORE surveillance tools are used without a warrant signed by a judge (the police grant themselves "warrants" covering unlimited uses for a period pending renewal, which I would have assumed constituted a "general warrant", something prohibited in UK constitutional law... but I am not a UK lawyer).

MI5, MI6, and NCA are immune to Freedom of Information, and you cannot sue in open court; you can take it to the Investigatory Powers Tribunal, who will not even let your lawyer see the relevant information to the case.