It was my friend Gill, who has a son in the same school as Louis, who pointed out that, according to this year's Parent Handbook, I am the new Media Studies teacher. "You dark horse," she said, and I asked what on earth she was talking about. "Look under the list of teachers," she said. And there I was. Or there I seemed to be, albeit with the addition of an extra L to my name: "Rebecca Tyrrell," it said, "Media Studies".

Matthew was thrilled when I told him. "It's simply marvellous," he said, "I could not be more thrilled for you. It is just the most tremendous news."

"What do you mean?" I spluttered, "it's clearly some mistake. It's not even the right spelling of my surname."

"That doesn't mean anything," said Matthew. "People are always misspelling your name. Even your publisher – even you – have been known to add the odd consonant."

He was right. An entire print run of these columns had to be pulped because they spelt my name with an extra L. And I applied for a passport with an extra R. "But I don't know anything about the modern media," I wailed. "Surely people are supposed to have a degree in this kind of thing? And no one asked me to be the new Media Studies teacher. I certainly don't remember applying."

"Ah, but we can be a bit forgetful these days, can't we?" said Matthew, in a voice that would suggest he was talking to a 108-year-old. "And it's definitely you. No question. I mean what are the odds on someone with your name, which is not a terribly common one, teaching Media Studies at the very school that you, a media person, send your own child to? No, it's definitely you. But don't worry so much, it will be a very informal, part-time thing, probably no more than a couple of hours a week, and you'll just have to pitch up and tell a bunch of teenagers some old Fleet Street anecdotes – life before Wapping, the time you interviewed Joan Collins, Rod Stewart, that sort of thing. It might be worth a phone call to find out how much you will be paid and how much of a discount we will be receiving on the fees. Be sure to get the discount. It's great news."

I am sure Matthew is wrong. I am sure there is more to Media Studies these days than how to interview a celebrity and how we took armoured buses through the picket lines in 1986. And what about the internet? There's blogging and downloads and just one week to go till the beginning of term. Mind you, there have been times, while out shopping for Louis's uniform and stationery, that I have experienced little surges of excitement about my new post. In fact, I have bought myself a pencil case and a new fountain pen for marking and some folders. I resisted a Prada briefcase, thinking I would see how the term progressed. Perhaps, I thought, I could ask for one for Christmas.

Part of me was actually enjoying the start-of-the-new-school-year collywobbles. But, to be honest, most of me was becoming more and more alarmed at the prospect, not so much of standing up in front of a class of teenagers, but of spending any time at all with Matthew, who was being tirelessly patronising. He gave me a book by Harold Evans, called Good Times, Bad Times, which was written, I pointed out to him, in 1984.

I tried calling the school to see if I could glance at the curriculum but, and I suppose it's because of the holidays, I got no further than an answerphone.

Two days before term started, however, I could go on no longer. There must have been a mistake. Think about it. I would have had an interview. Surely I would remember having an interview. Media Studies teacher is a proper, responsible job. And anyway, what was I supposed to do? Just turn up on the first day of school wearing a mortarboard?

Finally, the phone at the school was answered, and without asking whom I was talking to, I said, "I am Rebecca Tyrrel and I am ringing to explain that I have given the Media Studies job a lot of thought but, despite my weekly newspaper column, my long and varied newspaper career and my industry award, I really don't think I am the right person. I am afraid I will have to let the school down."

"I am sorry, who is it you want to talk to?" said the person on the other end.

"Well," I said, "my name is Rebecca Tyrrel and..."

"Would you like me to put you through to Rebecca Tyrrell?"

"No, you don't understand, I am Rebecca Tyrrel, and..."

"No, hang on, you can't be Rebecca because I can see her right now in the corridor outside my office. I'll get her for you, shall I? Although, just to let you know, she has married since the Parent Handbook was sent out and will now be known as Mrs Rebecca..."

"No," I said, "Please don't bother her. The problem has been solved."

I experienced mixed emotions when I put the phone down. I felt a little sad at the diminution of my uniqueness, although, of course, I always knew there must be other Rebecca Tyrrels, or even Tyrrells, in the world or even the same borough. I also felt a tremendous sense of sorrow that I hadn't bought that Prada briefcase while I had an excuse.

Matthew, on the other hand, felt nothing but an inconsolable grief that there was now no possibility of a discount on the school fees.