How do you solve a problem like Father Christmas? Even for a guy whose look was styled by a fizzy drink marketeer in the 1930s, he really has sold out. On the telly, advertising turkeys, in the shopping mall, making personal appearances. Soon he’ll be launching his own scent. Talk about devaluing the brand. If the old boy’s not careful, people will stop believing in him.

Preserving the image of a kindly gentleman who, despite a conspicuous obesity problem (surely it can only be a matter of time before a government directive requires him to slim), skips around the night sky delivering presents is an increasing headache for parents. When I was a girl there was no telly (well, none that I was allowed to watch), and no children’s advertising. There were no “secret Santas” at school, no catalogues popping through the letterbox and, crucially, no internet. It was possible to get to 8 or 9 without questioning Father Christmas’s existence; nowadays six-year-olds give you “sad-do” looks if you mention him in front of their mates.

Even in those who still believe, the exercise is heavily commercialised. I recently asked a five-year-old whether he had posted his letter to the North Pole. “Oh yes,” he replied, “and this year I’ve made it easy for Father Christmas.” What, only one present? “No, silly, I’ve written down all the catalogue numbers.” This raises the question of whether Father Christmas is a manufacturer or a shopper. I suspect the elves’ union (IMPS, Icelandic Miniature People’s Society, patron Tom Cruise) may have something to say . . .

But Father Christmas still represents a major milestone in the journey towards adulthood. If you stop believing in him, you stop believing in a lot of other things, such as that eating your hair will give you furballs, and that broccoli is the favourite food of fairies. This is one of the reasons that parents are so keen to preserve the conspiracy of silence. That, and the opportunities for blackmail. Bedtime and toothbrushing are so much easier in the run-up to Christmas – I have Father Christmas’s mobile number, see. One call from me and it’s goodbye Barbie Fairyoke Wings.

But you do have to be careful. I have a friend who talks about the moment she was told it was all a lie as one of the most humiliating of her life. Her tactic with her own kids has been to gently sow the seeds of doubt. She began by telling them that the Easter Bunny didn’t exist. This they took well (once they ascertained that there would still be chocolate). Currently, the questioning goes: “You will tell us, won’t you, by the time we are grown-up, whether Father Christmas is true – otherwise our own children might not get presents.” That’s the infallible logic of children for you.

I think there is something to be said for teaching children to deal with ambiguous truths – after all, that’s what much of being an adult is about. My response to “is Father Christmas real?” is: “That all depends on whether you believe in him.” Now, where did I put the catalogue number for that Furla handbag . . .

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