The security services can expect a full mailbag from S&M enthusiasts volunteering to be the victims of their next sting operation. This follows Sunday's extraordinary revelations that an MI5 officer's wife was one of the prostitutes involved in the infamous sado-masochistic orgy with Max Mosley, the beleaguered head of Formula One's governing body - and subsequent speculation (quickly denied) that the News of the World exposé had the official backing of the security services.

Despite the growing scale of innuendo and conspiracy theory that has materialised in cyberspace, many of us will feel inclined to believe the protestations of innocence emanating from MI5. What with Gordon Brown struggling to get his legislation for an extension to pre-charge detention through Parliament, spooks surely have better things to do with their limited time than loitering about outside a southwest London basement apartment hoping to catch a upper-middle-class gent with his pants around his ankles and a few bruises on his behind.

“We expect high standards of behaviour from all staff at all times, both professionally and privately,” an official said at the weekend, in reference to the MI5 officer who was forced to resign. “In any case where a member of staff is believed to have fallen below those standards, action will be taken.” We may assume that these standards are also applied to spouses, although the spokesman was not specific as to which of the prostitute's activities was objected to by the scions of morality in Millbank.

Was it spanking Mr Mosley's bottom or taking money for doing so? Reference was made to the susceptibility of the officer to blackmail, but we may wonder why this is relevant if he is not merely unashamed of his wife's proclivities but gets off on them.

What worries me is that the steadily expanding collateral damage of the Mosley affair might soon embrace the rest of us. I mean, if individuals are getting fired, or being forced to resign, for their private sexual preferences, and those of their wives, what does that portend for the rest of us when our predilections differ from those of the majority?

John Stuart Mill argued that the guiding principle of democratic society is that citizens should be free to make their own choices, unless and until such choices present a danger to other citizens - and he was not referring about the dangers posed by leather paddles and handcuffs. The freedom to engage in behaviour that meets the approval of the leader writers of the Daily Mail is no freedom at all.

This is why the looming decision on whether to sack Mr Mosley represents a more important barometer of our commitment to freedom than the success of otherwise of Mr Brown's attempts to extend pre-charge detention from 28 to 42 days. The latter is, at least in part, an argument about the balance between individual liberty and public safety; those of us who oppose the policy do so on practical as much as on ideological grounds. But the proposed sacking of Mr Mosley has nothing whatever to do with balance, proportionality or anything else. It is a naked (if you will forgive the phrase) attempt to punish a man because his private behaviour happens to disgust the rest of us.

The fact that you are unlikely to see Shami Chakrabarti popping up on Channel 4 News to defend Mr Mosley is precisely the reason why we should be so appalled by the mounting ramifications of the affair. Freedoms are never more vulnerable (or intolerance more insidious) than when nobody notices that they are under threat. Who in their right mind would want to defend a man whose father was a Nazi sympathiser and who gets his kicks from humiliating, and being humiliated by, leather-clad women?

This is precisely the kind of question that sluggish liberals asked themselves in the 1950s when the victims of mob injustice were not ageing sado-masochists but gays.

Prominent Jewish figures have argued that Mr Mosley should resign because his alleged re-enactment of concentration camp rituals was insulting. Call me pernickety, but how can someone be taken as insulting when his actions took place behind closed doors and were not intended to be seen by Jews or anyone else? Had Mr Mosley merely fantasised about his Nazi fetish, would that have been a resigning matter? Have we arrived in the dystopian environs of 1984, 24 years too late?

We must not delude ourselves that the maltreatment of Mr Mosley is of minor consequence because it does not involve the apparatus of the State. That kind of spurious reasoning is the last refuge of the bigots and the bullies. If the past few centuries of human history tells us anything, it is that public sentiment, not the law, determines the quality of life of those who dare to live a bit differently (or just look a bit different) to the majority. The working life of my father, an immigrant Pakistani, was made a misery by colleagues - but none of them, so far as I am aware, behaved criminally.

We are all of us at perfect liberty to shun, ridicule, berate, exclude or spurn fellow citizens, and a jolly good thing, too: nothing would be more atrocious than legally enforced tolerance. But if we are serious in our belief that individual liberty must be protected against incursions by the State, we must also accept identical responsibilities arising in our private relationships, whether we are hanging out with blacks, Jews, gays, Muslims, drop-outs or middle-class sado-masochists.

Sacking a person who is doing a good job because you disapprove of what he does in the privacy of his own dungeon is the first step on the road to serfdom.

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