E Jane Dickson: We love to hunt down fakery. But is it worth it?

Either the British security service was complicit in cruel treatment or not

There's nothing like a conspiracy theory to get Britain going. "Symbologists" of the Dan Brown persuasion are excited by the decision to open a 17th-century tomb in order to establish that, in fact, Shakespeare wasn't Shakespeare at all.

The theory that some of the plays and sonnets were written by the Elizabethan courtier and poet Fulke Greville has been knocking around for years. I have neither the interest nor the authority to dispute this – I'd say it was damned cunning of Fulke Greville to throw four centuries of Shakespeare scholarship off the scent with a signed corpus of rigorously splendour-free poetry, but then I could be falling for the old double-bluff.

I'm not sure what it proves, either, if Fulke Greville's monument does in fact turn out to contain, as billed, a manuscript of Antony and Cleopatra, the mortal remains of Philip Sidney and a scurrilous biography of James I. (A whiff of royal scandal is the triple-word score of conspiracy theorists.) The same monkeys who are at some point in infinity going to bash out the complete works of Shakespeare could doubtless come up with "conclusive" proof that said works were written by Simon Cowell. It is enough, for me, that somebody wrote those plays and that they are beautiful. And while there is a respectable body of "anti-Stratfordian" scholarship, much of the controversy buzzing on the web seems fuelled less by vexed notions of authorship than by the delicious possibility of a 400- year "cover-up".

We are all now ardent seekers after the truth. Hunting down fakery has become our new national sport, yet the game is rarely worth the candle. In 2007, the BBC was brought to its knees by the revelation that footage apparently showing the Queen walking out of a photographic sitting in a strop was faked. (In fact, her Serene Majesty was walking into the sitting in a strop.) Cue rolling heads and much public agonising about "truth in television". It only needed "Socksgate" – and who can forget the trauma of finding out the Blue Peter cat had been misnamed? – to establish a whole new culture of puritan zeal with "accountability" as its watchword. One can only guess at the distress of Channel 4 viewers who recently found out that the stars of Celebrity Come Dine with Me were not necessarily filmed in their own lovely homes, but I don't doubt an acceptable scale of compensation is even now being drafted.

Even advertising came in for a public drubbing when it turned out that Cheryl Cole's million-dollar locks had started out on someone else's head. (Moral to indigent hair-sellers: she's worth it, you're not.) Nobody said, "It's an advert, you're not supposed to believe it." Instead, there was an earnest drone of concern about how this kind of "dishonest advertising" was setting up unrealistic aspirations in young girls – no mention, in this regard, of her utterly authentic skinniness – and it was a mercy that the marginally-less-lovely-than-she-seemed Cole was not found tied to a lamp-post with her offending head shaved.

We teach our children that truth is an absolute and we know it isn't true. Some truths matter more than others. The eternal truth of Shakespeare has little to do with provenance. Entertainment is edited, advertising exaggerated. Daily life is punctuated by what Thoreau called "consistent expediencies", and our brains are hard-wired to process them. We, most us, understand that the "right" answer to "Am I fat?" is "No, you're lovely". ("Do I look fat in this dress/shirt/lipstick?" requires a subtler response.)

At the other end of the truth/expediency continuum, there are times when only the whole truth will do, when "cover-ups", gloss them as you may, are tainted by the sordid facts beneath. There is no hint of half-enjoyable frisson attached to the rumours of conspiracy now unfolding around the torture of Binyam Mohamed. Either the British security service was complicit in the cruel, inhuman and degrading treatment by the CIA of a British resident, or it was not.

As recently as June this year, Foreign Secretary David Miliband was unequivocal: "I can say quite clearly that the security service does not torture people, nor do we collude in torture or solicit others to torture people on our behalf." Following this week's ruling by three senior judges ordering full disclosure of information shared by MI5 on Mohamed's case, Miliband was already up to his ankles in expediencies, invoking the greater good of national security and the "control principle" whereby "information shared by us will be protected by us".

In recent years there has been a steady trickle of allegations relating to MI5's knowledge of the ill-treatment of detainees in Pakistan, Bangladesh, Egypt and elsewhere. Mohamed's case brings us to a moral crossroads. Either we support "the culture of suppression" alluded to by Lord Neuberger, Master of the Rolls, in his judgment against the security service, or we turn up the searchlight on the darkest corners of our administration.

It was Shakespeare (or someone posing as Shakespeare) who said, "Foul deeds will rise, though all the earth o'erwhelm them." In the brave new world of redaction and control principles, we must hope he was right.