Once again, it started with a telephone call a long, long time ago. Would I be interest- ed in doing Celebrity Mastermind? Like most things that I'm asked to do far in advance, I agreed, and then sort of forgot about it. Until about two weeks ago, that is, when I noticed a frightening-looking reminder in my diary. To make things even worse, I was having problems with my "specialist subject".

If you're a tad egotistical, as I am, then you have maybe given some thought to what your subject might be, along with your Desert Island Discs choice, and what you'd wear to meet the Queen when she knights you for services to... stuff. For me, it was always Tintin. I love Tintin and have read all the books so many times that it was an obvious choice. But then, disaster... Channel 4 commissioned me to make a film about my Belgian cartoon hero. I realised that if I went on Mastermind and got "nul points" then they might change their minds and boot me off my dream project. So I made a change and went for The Presidency of Jimmy Carter.

I'm still not exactly sure why. I do love American politics and have always been interested in Jimmy Carter, but it was hardly a specialist subject. I had a rambling theory about how, because he shared many similar views with Barack Obama and what with him being viewed as a not-too-successful president, this might be a warning from history. Also, and more important, he was a one-term president and, therefore, there was less to learn. So I did a bit of swotting and asked people on Twitter to test me, but the nearer the event, the more nervous I became. I had visions of floundering, like the unfortunate Minister for Higher Education, David Lammy, and starting to answer that Marie Antoinette had discovered penicillin. I imagined drying up and being unable to speak while John Humphrys lacerated me with a withering stare. I started to have terrible dreams where I'd wake up screaming, "Carter suffered from stagflation and his dog was called Grits!"

Finally, the day of filming arrived and I got to the BBC, a ball of nervous tension. They wouldn't tell me who my opponents were and I was eager to find out. My secret wish list went: Eddie the Eagle, someone from a soap opera and any footballer. I was out of luck. I checked the list in make-up – John Bird, the satirist, Mishal Husain, the newsreader, and Michael Winner, the film director. I felt a nervous rash start to form all the way up my back. This was a tough bunch, with no slack.

We all met up for the first time in a little side room just off the main studio. John Bird looked confident but started claiming that his memory was going. He was playing a clever game, the sly silver fox. Husain looked confident, almost relaxed. Winner appeared a little more cagey. Admittedly, this might have had something to do with a little fallout we'd had about four years ago after he agreed to be in one of my shows. We hadn't spoken since, but he was perfectly civil. I couldn't help wondering whether his specialist subject was going to be himself. I thought it best not to ask. Then, at last, in came the inquisitor, John Humphrys. There was a little banter between us all and a last-minute attempt at some insouciance from me that didn't really ring true. Suddenly it was time.

One by one, we entered the studio and took our seats on the familiar set. It all felt a little dream-like, almost an out-of-body experience. Then the music started and it was all too real. The spotlight hit the black Eames chair and we were off... there was no turning back for any of us now....