In the whole panoply of human idiocy is there anything so ridiculous as the outrage that occurs whenever people are reminded that spies spy? There was just such an outburst recently when Edward Snowden left his job as a contractor to the CIA and NSA, repelled, he said, by the discovery that surveillance programmes carry out surveillance. Snowden discovered that American and British intelligence agencies were involved in data trawling and was so horrified that he found it necessary to flee — first to the freedom-loving People’s Republic of China and then, to seek asylum, to Moscow. On the left of the political spectrum he is the new Julian Assange — though without the sex-crime charges.

Happily the new head of MI5, Andrew Parker, used his first public speech this week to inject some sanity back into the debate, and it was high time too.

As Parker reminded us, the intelligence services search for information not because they long to snoop on ordinary people, or feel a compelling need to read every email we send — but because they seek to thwart people who intend to harm us. We have enemies; there really are thousands of people hell-bent on blowing us up, and spooks exist to stop them.

The intelligence services don’t read emails at random, they focus their attention only on those who are of interest to them. Sometimes it seems as if we actually want to believe we’re all being spied on, to make us feel more important. But the truth is that unless you spend your vacations fighting jihad abroad, no one’s watching you.

And even if you are a frequent flyer to Kabul, it still doesn’t mean that every area of your life is being snooped on. As Parker said, ‘Being on our radar does not necessarily mean being under our microscope. The reality of intelligence work in practice is that we only focus the most intense intrusive attention on a small number of cases at any one time.’

And we should be exceedingly grateful that they do; but instead, we choose to bleat. Certain newspapers not only allow, but encourage, a culture of leaks which damage national security — and for absolutely no visible gain. Just as the Pulitzer Prize in America is most easily won by printing information that puts American lives at risk, so a branch of journalism has grown up here in Britain which regards the highest prize as facilitating a national security leak. One of the oddities is that this should be true now, at a time when a detailed intelligence-gathering capability has never been more necessary.

Intelligence agencies around the globe are currently battling with a problem which is unique to the modern world — the extent to which problems in one country spill over into others. A British convert to Islam may head to Kenya to take part in a terror attack. Or a terrorist trained in Somalia can head to Denmark. Both have happened recently. Distance is no longer an obstacle, and the number of theatres in which people can train and gather experience of fighting has grown exponentially. The problem has become, in Parker’s understated words, ‘more diffuse, more complicated, more unpredictable’.

At a discussion in Parliament last week organised by the Henry Jackson Society, General Michael Hayden, the former head of the CIA, said that the number of foreign fighters currently flooding into Syria is ‘twice that of the historic high in Iraq’. This includes a significant amount of young British Muslim men and women. Some will die in the process. Others will return and bring not only their experience but their ambitions back here to infect others.

So the intelligence agencies just have to be allowed to do their work. Rest assured, contrary to popular myth, they cannot act outside the law; they are not allowed to bump people off James Bond-style, nor detain people at random. In fact they work in an environment as strangely obsessed with health and safety and workplace oversight as any other. But they have a job to do which is rendered impossible if it is subjected to the current fashion for full transparency and disclosure.

Incidentally, when I asked if there was anything more ridiculous than outrage over spies spying, the answer is ‘yes’. It is those people who complain after any ‘successful’ terrorist attack: ‘Why did our intelligence services not know?’ The striking thing is that it’s often the same people who complain in both cases.