I think that certain departments such as MI5/6 should have some access to whatever they need to do their job. I'm not quite sure how that should be regulated though.
This is what I think. There's a huge difference between finding out if, say, you've pirated something, or you're claiming for £20 extra benefits you're not owed, compared with matters of national security like bomb plots and opposing agents attempting to damage the country.
Certain security services deserve to have access to anything and everything they need to protect us from exterior threats. I'd hope that this kind of power would be used selectively and sensibly by those involved, seeing as how they're our security/intelligence services, and not the insecurity/dumbarse services. I doubt an intelligence officer gives a fuck how much goat porn one bloke watches.
But then who watches the watchmen? And who watches the watchers of the watchmen? And who watches the watchers of the watchers of the watchmen? (And so on ad infinitum...)
