Philip Hensher: The Cameron dilemma for impressionists

That thoughtful and accomplished comedian-impressionist, Alistair McGowan, has said he is quite unable to imitate David Cameron. After repeated attempts, "all that comes out is an upper-class whisper". It's true: has anyone succeeded in capturing Cameron's way of talking, or even in isolating any characteristic gestures? His voice doesn't sound "upper class" to me: it sounds neutral, relaxed, and middle class, like a BBC announcer from the 1970s. He is remarkably free of verbal or physical tics, as far as I can see; there is little on the surface to ridicule.

Compare the bundle of mannerisms of Gordon Brown: the bizarrely out-of-sync smile and the chewing on air. Or Peter Mandelson's manner of speaking, the cooing of a man who was once told that if you want to get people to listen, you lower, not raise your voice. Or Ann Widdecombe, or Boris Johnson, or John Prescott, or Tony Blair, or Ken Livingstone, or William Hague, or Lembit Opik, or Kenneth Clarke; all well-loved bundles of interestingly unique appearance and what used to be called an inimitable way of speaking, by which was meant "highly imitable".

What is it in people that makes them subject to the caricaturists', the impressionists' art? Some politicians are, some aren't. How the French caricaturists must have prayed for a Sarkozy victory in the last French election. The prospect of having to draw the well-made blandness of a Ségolène Royal for the next five years must have been a nightmare. Yet Sarkozy, with his interesting, rubbery face, his well-aired complex of high-heeled shoes and imperious vanity, practically drew his own caricatures, as do Vladimir Putin and those worrying bun-faced twins who appear to run Poland.

When a figure with this secretly ridiculous centre departs, it is a nerve-racking time. George W. Bush, memorably depicted as a knuckle-dragging ape by Steve Bell, also had the sort of voice which tempted everyone from the playground upwards to have a go. Obama, as far as I can see, is still defeating all such attempts. Similarly, Angela Merkel just doesn't seem very easy to translate into caricature, with her middle-of-the-road appearance.

In these cases, it's not necessarily to do with a nervousness about venturing away from white male politicians, or simply not wanting to imitate generally admirable figures. After all, comedians had no difficulty in imitating what, to us, are Nelson Mandela's highly recognisable tones, and both the admirers and the denigrators of Margaret Thatcher were very ready to take her off at a moment's notice.

No, it's something to do with a personality worn on the outside. I have a dear old friend who has such a characteristic style that the mere mention of his name sends his social circle off into lewd impersonations. And a politician who can make a mark on an electorate, or an impressionist, by his style is surely at an advantage. Or used to be. You notice that my list of politicians of interestingly unique manner is mostly made up of people who made their reputation in a previous political generation.

If David Miliband takes over as leader of the Labour Party, we will have three party leaders of respectable, well-scrubbed middle-class appearance, and a large group of cartoonists and impressionists holding their heads in their hands.

I more or less stopped going to Hollywood movies when I realised I was quite incapable of telling one blonde starlet from another – I just could not remember what Katherine Heigl or Scarlett Johansson looked like. And in the same way, the electorate's demand for soothing, well-spoken, convincingly middle-class but indistinguishable representatives may be reconcilable with the requirement for high-quality minds. What it doesn't do is turn up a face that Gillray could have worked with.

Letterman: a victim of the tyranny of byte-size blackmail

The talk-show host, David Letterman, detailed, live on his own television show, an appalling attempt to blackmail him out of $2m (£1.25m). The story involved – had to involve – Letterman explaining the basis of the blackmail, which basically added up to his own sexual misdemeanours with female members of his staff.

Most people over 40 will have been amazed at Letterman's decision to go as public as this. When someone is blackmailed over their own bad behaviour, the law goes to great lengths to protect the victim's name. Otherwise, it is concluded, the blackmailer has succeeded, and what the victim most feared has come to pass.

So why didn't Letterman go to the law, and let an anonymous blackmail trial run its natural course?

The reason is, of course, that these days, it would be completely impossible for someone of Letterman's status to remain anonymous for the entirety of a blackmail trial. The internet knows no contempt of court, no restriction of free speech, no binding orders. Letterman was probably right to conclude that, since the facts were going to become available anyway, he might as well be in charge of releasing them, as publicly as possible.

A blackmailer's threats are now more powerful than ever before, it appears; his victims, it seems, cannot do anything without acceding to their demands or releasing the damaging information on which the threat depends.

Sex abuse by women is not a numbers game

In the wake of the abuse case in Plymouth, in which a female nursery worker, Vanessa George, abused children and circulated images of the abuse to another woman, people have wondered how prevalent female abuse is.

Enter the Lucy Faithfull Foundation. It is a child-protection charity that deals with British female sex offenders. It claims that its research "confirms" that "up to 20 per cent" of "a conservative estimate of 320,000 suspected UK paedophiles" were women. That enables a headline shrieking that 64,000 women in the UK are "child-sex offenders".

More realistically, we can say that the figure of 320,000 is a casual estimate; that the figure of one abuser in five being a woman is impossible to verify. Compare these figures with the Government's figures showing 56 female abusers in custody and another 84 in the community. These include cases such as de facto consensual affairs between just-adult women and those just under the age of consent, which seem very far removed from the George case.

No doubt abuse is under-reported, and one case such as this is very shocking, but I find it impossible to believe 64,000 female abusers are roaming the country. It seems grossly irresponsible of foundations such as this to cite figures in this way. It adds greatly to the atmosphere of terror and excessive caution in which children are brought up.