Psst, want to see some snaps of my kids?

'It was probably Cherie's mother who insisted on sending family snaps to the press. Grannies are like that'

But St Peter, I hear myself wailing at the Pearly Gates, I had no idea I was ruthlessly exploiting my son when I had pictures of him dressed as a chorister sent out to all my friends one year instead of Christmas cards. He looked so angelic, I thought it might encourage more people to go to church, I finished lamely. With a brusque gesture St Peter dismisses my excuses. If Iain Duncan Smith, the leader of Her Majesty's loyal Opposition, says that using pictures of your children to further your political ambition constitutes ruthless exploitation that's good enough for us, he growls.

It was granny, if I remember, who suggested using the snap of wee Jim looking angelic in his crimson surplice as a substitute Christmas card. It was probably Cherie's mother who insisted on sending happy Blair family snaps to the press. Grannies are like that, but bearing in mind my usual contempt for all those who transform chocolate-box portraits of their kids into greeting cards, I'm surprised I agreed to it.

One year we received a holly-trimmed card showing a friend's four small children, the three older ones dressed as magi looking down on baby Oliver lying in a Mothercare manger.

Choirboys in full regalia, on the other hand, are genuinely seasonal like robins and reindeer. But if I'm honest, I will admit to a hidden agenda. You get kudos, brownie points and respect if people know that your son is a chorister. How well, how sensibly, they're bringing up that child, people say. Not, alas, that it did us much good in the end. Three years into his choral years, wee Jim was unceremoniously booted out for his involvement in a disgraceful incident at Lambeth Palace.

Details of the affair are still murky, but the outcome is beyond doubt. The door of the Archbishop of Canterbury's lavatory was locked (fortunately the prelate was not within), the key went mysteriously missing and three choristers – yes, wee little Jim included – were apprehended, sent for trial, found guilty and, despite a strenuous campaign to save the Lambeth three, dishonorably discharged. Mr Duncan Smith will appreciate that story no doubt. Ruthless exploiters of children will get their comeuppance in the end.

So where does this leave the poor Blairs? Should they, like Madonna, eschew all photographs of themselves with their children. I know about Madonna, incidentally, because, as I've mentioned several million times, Guy Ritchie's dad is an old friend of mind. "How's Rocco?" I asked last time we had lunch. The proud grandfather handed over the usual clutch of bouncy baby snaps, Rocco scratching his nose, Rocco looking pensive, Rocco looking... ooh yes, exactly like his dad. Why aren't there any pictures of Rocco with his mother I asked surprised. Don't be daft I was reprimanded. If someone got hold of a picture of Madonna and child they could sell it to one of those celebrity magazines for a fortune so she prudently does not allow any to be taken.

I was tempted to say that if I had Madonna's millions I wouldn't care if someone seized the opportunity to make a few bob on the side, but I held my tongue. Old friends are precious. And so are children, which is why I am puzzled by Mr Duncan Smith's outburst. He, as you know, has four children, and one wonders what he would do if he moves into No 10. Will he declare it a child-free zone and send Betsy and the children to live elsewhere so that there's no chance of a lurking photographer snapping any of them.

There are a great many more ruthless ways of exploiting children than taking happy holiday snapshots of them. If the Blairs weren't a happy family and this was a cunning cover-up to make them look as if they were, that would be different. Alas this is not the case. They are, by all accounts, sickeningly happy – Cherie helps Euan with his homework, Tony buys his daughter trainers, they all sit around playing Monopoly together at weekends. Cynic that I am, I sometimes feel that if they were slightly less than the Swiss Family Robinson they would relate more to the rest of us.