MI5 feared GCHQ went 'too far' over phone and Internet monitoring (guardian.co.uk)

> The source claimed that even the conventional warrant system has been distorted – whereas police used to ask for a warrant before intercepting a target's communications, they will now ask GCHQ to intercept the target's communications and then use that information to seek a warrant.

This method of getting a warrant completely subverts reasons a warrant is required. It turns a warrant into a sham.