It was Richard Crossman who in 1971 called secrecy the "real English disease". "Real" because at that time the English disease was generally supposed to be strikes. Government secrecy  which this book is about  blanketed vast areas of British public life for most of the last century, upheld by a fierce and undiscriminating Official Secrets Act, passed through parliament by underhand means in 1911 (the government of the day pretended it was just to stop German spies), and by the gentlemanly code of those in the know. The latter were so secretive that the rest of us weren't even told what was being kept secret, with the very existence of agencies such as SIS, MI5 and GCHQ remaining hidden. (Of course a lot of people guessed.) Thus armed, a supposedly democratic state could  the argument went  keep us safe from foreign plots, and also  though this was less trumpeted  from domestic subversion: for example, through strikes. If anything, the growth of democracy made this worse, because it threatened to undermine the elite's exclusive control over politically sensitive knowledge. In all the battles over secrecy detailed in this book, a class-war element is obvious. It was them  the elite  against us. (Or us against them, the plebs, if you've strayed over here from the Times.)

It wasn't, however, the plebs who first started spilling the beans. The upper classes have always relied too much on their own closed system of "honour": witness MI5's notorious failure to credit that the Cambridge-educated Kim Philby could be a traitor until it was too late. Some early whistle-blowers did come from the middle and lower orders of society, which the civil service was forced to trawl for recruits as it expanded, but the worst offenders were some of the elite themselves. It started with Churchill's and Lloyd George's post-first world war memoirs, which broke all the existing rules about divulging secret documents and private cabinet discussions, but couldn't be reined in because their authors were so high and mighty. That afforded the precedent for others: "If them, why not us?" A second breach was opened after the second world war by journalists, and especially Chapman Pincher of the Daily Express, who is the undoubted hero of this book. Moran has interviewed him extensively, and appears to trust his every word: "at the risk of sounding sycophantic", he writes at one point, which I'm afraid he does, rather. It was Pincher who sparked the "D-notice" affair in 1967 when he revealed, in defiance of a D-notice  the semi-formal device that was supposed to prevent this sort of scoop  that the state was routinely intercepting private cables and telegrams. Moran calls this "the British Watergate", though that seems an exaggeration. Thereafter "investigative journalists", aided by aggrieved civil servants, started queuing up to dish the spooks.

The government at first responded by wheeling out its major weapon, the Official Secrets Act, but with some embarrassing results. The D-notice affair was one. Another was Thatcher's pursuit of Peter Wright over his memoir of his time in MI5, even as far as an Australian court of law (albeit on a different charge), where it came to an ignoble end. Thatcher was an absolutist when it came to secrecy, as with much else. So was the cabinet secretary Burke Trend, who supported the existing Official Secrets Act as a deterrent, much like the "cane in the best type of orthodox school". So we know where he came from. They were both wrong, and it wasn't long before the other ex-public schoolboys in Whitehall came to see this. So they adopted another strategy entirely, which was to open government up to an extent, but always in ways they could control. The new Official Secrets Act of 1989 removed some of the more ridiculous aspects of the old one  such as forbidding the revelation of anything that was done in Whitehall (paperclip purchases, for example)  but at the same time tightened it, by disallowing a "public interest" defence in the cases it still covered. Then they  specifically, the secretary of the D-notice committee - wined and dined journalists to appeal to their patriotism to keep stumm. Apparently even Private Eye was nobbled this way. Chapman Pincher was also kept on side by feeding him privileged information  not always accurate. Even more subtle was the wheeze of allowing certain academics and others access to the secret archives and permission publish from them, so long as they were "trustworthy"; that is, "writers would be selected for their willingness to portray things in a positive light". (Generally, anyway; you needed some criticism to make it convincing.) This culminated in a series of handsome "official histories" of the secret services (of which one of the most recent is Christopher Andrew's The Defence of the Realm, on MI5). Most independent historians are unhappy with this  Moran claims it's because of "the acid of envy"  but he thinks it's OK. A problem, of course, is that other historians are unable to check these books' findings, which is a slight problem with Moran's work too, with its occasional references to "private sources" and interviews with Pincher. The argument in favour, of course, is that it's better to have sanitised information than none. The government was allowed to appear more "open", and to bruit some of its secret services' undoubted wartime achievements, which the Americans just then were shamelessly appropriating (viz the later Hollywood movie U-571). That would be good for the spooks' morale.

So far as we know, this book hasn't been "authorised", but it occasionally reads as if it could have been. Some of its omissions are surprising: domestic surveillance of the left, for example, and derring-do in Ireland, both of which the secret services were nervous about, and may be thought to make them less trustworthy (and so less deserving of secrecy). Another is the radical press, which also played a part in unmasking their naughtier enterprises, but which Moran merely dismisses as "trendy". He has the conventional elite view of Harold Wilson as a paranoid conspiracy theorist, without making allowance for the venomous hatred that Wilson attracted among the classes who made up the secret services and controlled the press in his time. Moran may have got this from Pincher (Wilson certainly hated him). This bears comparison with the hostility that President Obama arouses among American Republicans, and for a similar reason: race in Obama's case, class in Wilson's. Moran also rather undermines his "paranoid" charge by confirming that Wilson's own D-notice secretary was, in fact, plotting with others to bring him down. One day we may look back on Wilson more charitably, especially in the light of those who followed him. Perhaps Moran is trying to establish his own "trustworthy" credentials for when the next tranche of secret-service history commissions comes along. If so, good luck to him. I for one won't be at all envious.

This is a well-researched and fascinating book, despite the blinkers. And it ends with a note of caution for those of us liberal historians who might otherwise naturally place ourselves on the "open government" rather than the "secret state" side of this argument. The more "open" government becomes  in the sense of its written records being available to everyone  the less likely our governors are to write things down. That will seriously cripple future historians and anyone wanting to find out how government works. For this reason, as Moran puts it, if WikiLeaks is permitted to reveal all, "society will have paid a very high price indeed for Assange's crusade". Whether that price outweighs the benefits of rulers having to act responsibly, because the people are watching them, is the central issue here.