David Aaronovitch: It is a trivial question, but politicians must answer

It's dark these mornings, and I'm finding it hard to wake up. So when an interview with a minister on the Today programme yesterday moved abruptly from the question of political correctness among social workers to that of the safeness of MMR jabs, I momentarily lost the plot. Or maybe it wasn't about the safety of MMR jabs at all. Because all of a sudden Jacqui Smith, junior Health minister, was accusing her interlocutor, John Humphries, of asking her "personal questions".

Now, there are some unsettling rumours circulating about Mr Humphries. For example I am told that following transmission of his On the Record show on BBC1 he has been known to empty the whole of the hospitality cheeseboard into his briefcase and take it home. Such are the tales doing the rounds, but I have never heard of him asking "personal questions"; the Llanelli lecher he ain't. Could he have winked and asked Ms Smith whether she enjoyed the occasional late sitting?

Actually the question was this: "Did your children have the MMR jab?" And when Ms Smith declined to answer on the basis that she wasn't going to discuss the health of her children, Mr Humphries put the question to her again and again, suggesting en route that she was being "holier than thou". It was, he told her, a simple matter of discovering whether ministers as parents themselves had real confidence in a procedure that they recommended to other parents. "My children are not elected to Parliament, I am – so I will answer for myself and for government policy," said an irritated Ms Smith.

I gather that the Health Secretary, Alan Milburn, was infuriated by this ambush, and it may be some while before the Today programme team gets another Health minister to help fill their shining hours.

Actually Ms Smith couldn't answer. In Prime Minister's Question Time on Wednesday, Mr Blair had already told a questioning Tory that the immunisation of his own son, Leo, was not a matter he was prepared to discuss. His questioner was Julie Kirkbride, Conservative MP for Bromsgrove, former Telegraph journalist, anti-MMR person and recent mother. On MMR, she told him: "The public want to know whether the Prime Minister practises what he preaches", and specifically whether the needles had entered the chubby person of the child she called "Little Leo". (A performance, when I heard it on the internet, whose sincerity reminded me of the smiling good wishes bestowed by the Bad Fairy at the christening of Sleeping Beauty.)

The public in this instance turned out to be (as it so often does for Conservative MPs) the Daily Mail, which has been campaigning for Cherie to answer the MMR question, and which rewarded Ms Kirkbride with a large photograph on page 4 of "Julie with son, Angus, now 14 months". Welcome to the public stage, Angus, like it or not. Keep your nose clean.

But even so, the question is whether or not Mr Blair is right to argue that it is none of our businesses whether Leo gets jabbed or whether he doesn't. Of course, put in this way the answer is obvious. Leo, however, is not the issue here. He may get the point, but he isn't the point. It is his parents who make the decision – why should they not tell us that they have as much personal confidence in the system as they expect us to?

Because it is the thin end of the wedge, says Mr Milburn, as well as sources in Downing Street. Once you start talking about what your kids do and don't do, then it is open season on anyone with a minister for a mother. Do your children practise safe sex, like what you say people ought to? The Express has interviewed Mandy, aged 16, who reveals that no condom was worn. No bike helmet either (The Guardian). The anti-smoking minister's daughter is on 30 a day (The Times). When the Mail recently ran a front-page story about the drug problems of Lord Irvine's 25-year-old son, citing the debate on cannabis as justification, this was the abyss opened up in front of the PM's horrified eyes.

In the video shops now is a movie that I saw in Arizona a few weeks back. The Contender is the story of a woman nominee for the vacant vice-presidency who finds herself up before the super puritanical chair of a Senate confirmation committee. He puts to her a series of personal, personal questions, which she refuses on a point of principle to answer. The President (Jeff Bridges) urges to her to do a Jack McConnell, make two clean breasts of it, and trust to the forgiveness of the American people. But she won't, and the climax to the movie is her televised statement about why such intrusion into the private lives of politicians damages the political process, trivialises public discourse, and discourages the talented from seeking office. She wins. Bill Clinton could have written it himself.

And, in a way, asking whether "Little Leo" has been jabbed or not does trivialise things. What, after all, does Cherie know that we don't? Nothing. Mrs Blair is not the mother scientist of the nation. On website after website you can find discussions about the possible correlation between autism and MMR in some children. As ever there are contrary minority scientific viewpoints, just as there were on Aids (wrongly) and BSE (rightly). The Department of Health has put out its own best guess. Jabbing or not jabbing Leo resolves nothing. Especially since, for all we know, he may be one of the kids who doctors anyway advise should not have the MMR vaccination. What are you going to do? Have his whole medical history read out in the Commons?

Our psychological need for certainty can also be portrayed as a bit pathetic. We want Daddy Tony and Mummy Cherie to hold our hands, and lead us firmly through the murk of a complex argument. We may not understand what Dr Wakefield or the GMC or the BMA are going on about, but if the PM is prepared to do it to his own kid, then that's good enough for me! You lead, I follow.

Pathetic, perhaps, but actually not that unreasonable. In this case what happens to the kid is decided entirely by the parents. If, in their capacity as ministers, those parents are engaged in persuading us that we all ought to do something, it is pretty natural to wonder whether they do it themselves. Of course this involves knowing what happened to the child.

Important, too, is the issue of hypocrisy. The example here is that of Patrick Jenkin, a minister during the three-day week, who had publicly advised that the nation should turn its lights out after dark to conserve energy, yet whose own house was photographed one night with practically every bulb in the place burning.

So Mr Blair should tell us whether Leo has had the injection, and then tell us no more. There is, after all, no inevitability, no law, that forces further sliding along the slope, or the admission of more of the wedge. And we for our part should recall Mr Gummer, Cordelia and the hamburger. All of which means that if it is wrong of Mr Blair to refuse to answer, it still doesn't make it a particularly useful question to ask.

David.Aaronovitch@btinternet.com