THE LibDems - or as they used to be called before the days of our modernisation, Liberals - have an unsurpassed reputation for claiming the moral high ground.

They have always boasted that they are not as other men - not like the Tories and Labour, full of class interest and prejudice.

No, the Liberals alone are the decent party, dripping with good causes and fair-mindedness. They remind me of Mr Bulstrode in George Eliot's great novel Middlemarch, where it is said that "He was either a Methodist or a hypocrite depending on the range of your vocabulary".

Because the Liberals seem always particularly partial to sleaze. Their greatest Prime Minister, Lloyd George, was a serial womaniser. There was the unseemly Jeremy Thorpe incident in the 1970s when the gossip was all about secret homosexual trysts and even murder. Remember dear Paddy Pantsdown who, after his well-publicised adultery, remained leader of the party - until he went off to Bosnia to command the moral high ground there as well.

And now Charles Kennedy and his "fight" with the bottle. I feel sorry for him, the way he has been treated by that gang of self-righteous muesli-scoffing, sandal-clad, holier-than-thou nonentities that make up the parliamentary Liberal Party. One might even say that Charlie Kennedy drunk is tons better than that lot sober. He did, after all, increase their seats in Parliament to a number higher than it's been since... well, since the golden days of Lloyd George in fact.

But the most irritating aspect of poor Charlie's demise is the very public airing of what is essentially a private matter. If Kennedy is incompetent, then surely he must step down. But the issue is just that - his competence or the lack of it. We don't need some forensic inquiry to explain just why he's alleged to be incompetent. We don't want this intrusion into his private sufferings. It's like putting the man in the stocks and throwing rotten fruit at him.

I mean, do we wait for the day when Blair's incompetence, his failure to reform the schools, the health service, transport, housing, pensions - you name it - is explained by saying he was bottle-fed and dropped on his head as a baby? Or is that nice Mr Cameron such a vacuous trendy, creep and sham because his elocution teacher - or his ballet mistress for all I know - used not to smack his bottom hard enough?

What plagues our public life is this constant parade of matters that ought to be private. Anyone complaining about Lloyd George's fornicating would have been told to mind his own business. Anyone nagging Churchill about his boozing would have been told to go and fight them on the beaches. And besides this unseemly publicity about everyone's private life, there is the medicalisation of morality. What always used to be regarded as character flaws or bad habits are now described as illnesses.

So one is not, for instance, a glutton but "suffers from" an eating disorder. A child is not just naughty but is afflicted by attention deficit hyperactivity disorder. The ultimate - I suppose, but watch this space - is the case of the teenage thug who murdered his parents and received a reduced sentence because he was "suffering from" narcissistic personality disorder. What's the difference between NPD and being an evil little prat? Satire is impossible these days. You couldn't make it up.

* Peter Mullen is Rector of St Michael's, Cornhill, in the City of London, and Chaplain to the Stock Exchange