Q: Do you agree with the prime minister who [supports Andrew Parker's warning that] the Guardian's publication of those files handed the advantage to Britain's enemies, it was a guidebook to terrorism, the Edward Snowden story.

NC: I certainly agree that if what you end up doing is just basically publishing very technical information that actually most Guardian readers, or most of us, would not frankly understand but the only people who will understand are the technicians amongst the terrorists, then what's the public interest in that?

However, I think of course there's a totally legitimate debate to be had about - and my experience speaking to people in the intelligence agencies is that they recognise this - the use of these new, incredibly powerful technologies. We have legislation, regulations, which were designed for an age which is quite different now. And both terrorists and states, and security agencies, now conduct this battle online in a way that was unimaginable a few years ago. And what they means for privacy and proportionality is a totally legitimate area of debate.

How you hold the secret parts of any part of any state to account is an incredibly important issue. Because secrecy is necessary, of course it is. You absolutely must defend the principle of secrecy for the intelligence agencies, without which they can't keep us safe.

But you can only really make secrecy legitimate in the eyes of the public if there is proper form of accountability.

Now, we've improved it. This government has taken big steps - and I'm delighted that we've done this - to strengthen, for instance, the intelligence and security committee, which is the committee which holds the agencies to account in parliament. But I saw a previous head of MI5 say recently to expect the public just to accept that some slightly opaque arrangement in Westminster is the way to hold everyone to account, in which the public does not have much of an insight - I think it's right for us to ask whether there anything more we can do to make sure the public feel that accountability is working in this area properly.

Q: But did the Guardian go to far with the level of detail it published?

NC: Oh, I've got no doubt that there were some parts of what was published which will have passed most readers of the Guardian completely by, because they were very technical, but will have been of immense interest to people who want to do us harm.

Q: So it should not have put it out there?

NC: As I said, I think it's a totally legitimate debate, about the power of these technologies, about how you get the balance right, how you make sure these technologies are used in a proportionate and accountable way, but I don't think just giving technical secrets, if I can put it that way, to people who want to do us harm, serves any purpose.