Never work with children or reindeer, the saying almost goes. The demeanour of five of the capital's Santas suggests why.
It's an odd convention that - once a year - allows small children to come into collision with strange old men in a grotto; that allows (no, demands) that Jessica and Joshua climb on the knee of someone they have never met before, whisper secrets in his ear and be given gifts in return.

Odd from the child's point of view. It is one thing to believe that an unseen but omnipotent man visits all children on Christmas night, leaving gifts. As with the tooth fairy, the mystery is complete; nothing can spoil it, unless a clumsy or drunken daddy be caught - arms full of presents - slumped over the fireguard, or impaled on the poker.

But to meet Father Christmas, to smell his smell, to touch his red coat with its white lining, to experience the human particularities of his grog-blossom nose, or his sagging jowls, his sad, bagged eyes or his faltering hands, must surely jolt the child out of any easy belief in the legend. To make faith even more difficult, the child is expected not just to encounter Santa once, but to meet him again and again, always in a different incarnation: at the department store, the school bazaar, the new, purpose-built super- grotto.

It is odd from Santa's point of view, too. Santas don't believe in Santa Claus (except the one in Miracle On 34th Street). By and large they have no personal stake in the children's belief in Santa, either. To some - the more professional - it is a warm, comfortable (if highly seasonal) way of making a living. They may even take a pride in the material of their costumes, the fluffiness of their beards, the timbre and resonance of their ho-ho-hos. To others it means a temporary shelter, a bit of spending money and company. For the amateurs it is the consequence of being press- ganged by tyrannical women, who will point out that they have done all the shopping, office party arrangements, cooking etc, and that the least a man can do is stick cotton wool on his face and be nice to the kids for half- an-hour.

But I wouldn't do it. The clothes are sweaty, the beard itchy, the children querulous and quarrelsome, the parents maudlin, the posture uncomfortable, the food poor, the drink non-existent, the pretence wearisome.

And I wouldn't do it because, somehow (odd this - oddest of all, really), it would spoil it for me. How can I be Father Christmas?