It's not often that top spooks emerge from the shadows, and on those rare occasions
when they do, they tend to choose their words very, very carefully. That's why we need to be just as careful when we examine what they say.
This week's speech by the director-general of MI5, Andrew Parker, was a text-book example, in which he described as "utter nonsense" the suggestion that security services "monitor everyone and all their communications". It was, you may think, a clear swipe at the US National Security Agency whistleblower Edward Snowden and The Guardian, which has been publishing his disclosures over the past several weeks, and which yesterday was described by the Daily Mail as "The paper that helps Britain's enemies."
But hang on a minute. At the centre of the mass of material that has emerged is not the allegation that the security people are monitoring everyone -- which would be patently absurd -- but that they have the capability to monitor anyone. It's not the same thing at all, as Mr Parker knows full well. He is, as you would expect, a master of the "non-denial denial", in other words, he is categorically denying something that hasn't been alleged.
Let's pretend this discussion was taking place in a pre-internet world. Out of the woodwork comes a security service insider who tells us that MI5 have entered into a secret agreement with all the country's major key manufacturers that enables them to open the front door of any house in the land, to enter any home, and to rifle through any filing cabinet and desk drawer. No search warrant required, no oversight in place.
Fine, you may say, be my guest. If they want to rummage through my underwear drawer, go ahead. I have nothing to hide, and nothing to fear. That's pretty much what many people have said on learning that US and UK security agencies have exactly that kind of access to our online world.
But now suppose you start a campaign to stop someone developing a fracking plant at the end of your garden, or a wind turbine farm on a nearby hill. You send out a few emails to your neighbours, discuss protest demonstrations, perhaps someone even suggests some direct action: sitting in the road in front of the mining company's diggers, maybe, or cutting through a security fence to plaster posters all over the site of the proposed development.
One morning, at 6am, there's a knock at your door. The police are there, armed with a huge fat file containing every single email you've sent over the past six months, all the emails you've received, all the books you've bought online and every Google search you've made. Come with us and answer a few questions, they say, or we may have to tell your partner about this online dating site you've registered with, looking for ... well, you can fill in the details.
Fanciful? Not at all. Ask the environmental campaigners who were spied on for several years by undercover police officers (some of whom even fathered children with the women they were spying on), or the supporters of the family of Stephen Laurence who found they too were being spied on. Nasty things tend to happen in the dark, when no one is looking -- and that's why it's so crucial that we have some honesty about what exactly the security agencies are able to do and under what kind of authority they operate.
I don't expect them to tell us every time they tap into the email account of a suspected jihadi bomber. I really don't need to know which websites they're monitoring, or which Google search terms set alarm bells ringing at GCHQ. What I do need to know is that someone, somewhere, outside the security bubble, does know, and has authorised the surveillance. In theory, that's what is meant to happen now. In practice, well, let's say there's room for doubt ...
We also need to know that the spooks aren't lying to us. There is, unfortunately, good reason to suppose that the NSA in Washington has not been entirely honest, even with members of Congress, when discussing what sort of surveillance capacity it has built up. We know from experience, alas, that if spies are allowed to operate without effective supervision, they do have a habit of going quite a lot further than might be considered appropriate in a society that professes to value freedom of expression and the right to privacy.
So here are a couple of suggestions for MI5's Mr Parker. First stop playing games with your non-denial denials. There's a serious debate to be had, and you need to be part of it.
Second, in the face of calls for greater oversight of what you and your colleagues at GCHQ are up to, tell us what kind of supervision you'd regard as acceptable. If the police need to apply to a magistrate for a search warrant before they start rummaging through my files, what would you regard as an appropriate equivalent safeguard?
It is mildly encouraging -- let's not get too excited -- that both David Cameron and Nick Clegg acknowledged yesterday that there may be a case for re-examining the safeguards that are in place at present. The prime minister said: "If people want to suggest improvements about how [the security agencies] are governed and looked after, I am happy to listen to those."
The concerns that have been expressed since Edward Snowden started shovelling out his secrets don't come just from pesky journalists poking their noses into matters best left to the security services. (And it's not just pesky journalists from The Guardian, either, as evidenced by the impressive number of statements published today from editors around the world who are backing its reporting of the Snowden material.)
In addition, such luminaries as Tom King, the former Conservative chairman of the parliamentary intelligence and security committee, the former director of GCHQ, Sir David Omand, and a former director general of MI5, Dame Stella Rimington, have all added their voices to those questioning whether it's time to tighten up the controls and allow a little more daylight into the world of the spooks.
On the other hand, today's Times (£) quotes Sir David Omand as saying that the Snowden disclosures are "the most catastrophic loss to British intelligence ever, much worse than Burgess and MacLean in the 1950s." (I suspect, though, that The Guardian's editor, Alan Rusbridger, may have had a point when he suggested a couple of days ago: "You would have to be a terrorist who didn't know how to tie his shoelaces not to believe that people were watching things on the internet and scooping up telephone calls.")
Andrew Parker said in his speech on Tuesday that the ability of GCHQ to intercept the voice and internet traffic of terrorists is "vital to the safety of the country and its citizens". He's absolutely right, and it is in the nature of his business that we will never know -- we can never know -- how many attacks such surveillance may have prevented.
What we need to know, and what we have every right to know, is that MI5 and their chums are being properly watched and supervised. Oh yes, and that they don't lie to their political masters -- or to us -- about what they're up to.