He defended the right of ministers, rather than judges, to sign surveillance warrants arguing that there is a "very strong political incentive" to authorise surveillance only when justified.
He said: "Perhaps it is a feature of the times that we live in, but I'm sure I can speak for all of my colleague who sign warrants that we all have, in the back of our minds, that at some point in the future we will - not might be, but will - be appearing before some inquiry or tribunal or court accounting for the decisions that we've made and essentially accounting for the way we've applied the proportionality and necessity tests.
"There is a very strong political incentive in the system to apply these tests narrowly and in a way that minimises the scope of the agencies to interpret warrants that are issues."
He denied that bulk collection of data by GCHQ amounted to mass surveillance. He said: "Mass surveillance is illegal. There are strict rules in place to make sure data collected is not used in any way. I think the immediate discarding of 99.9 per cent of the data does not give rise to intrusion."