He taught at Wandsworth Boys' School. When I started, it was still a deeply traditional grammar with a head boy who wore a cloak and was allowed to cane pupils. At the start of my second year, though, it became a comprehensive with a staggering 2,000 boys on roll.
There was such a mix of people there, from kids who should have gone to borstal, to kids who could have probably gone to Eton. We all wore uniform, and you weren't quite so aware of the different backgrounds - apart from the fact that you'd have one boy saying "Yer wot, Guv?" while another one's going "Pardon me!".
My first day happened to be John Clegg's first day too, which might be one of the reasons that we got on so well. His subject was music, but for the first two years he was my form teacher. He had rich blond hair and a chubby face, and he wore gold-rimmed spectacles. He loved crossword puzzles.
He could be quite fiery, and whenever he lost his temper his head would shine like a red light bulb - it was an amazing sight. I remember one of the boys making a hole in a piece of chalk and putting a match inside. Clegg went mad when it burst into flames. We all had to stay behind after school for three days and write lines.
When I first started at Wandsworth I felt a bit disoriented because the school day was so broken up. You'd have biology with one teacher, and then you'd be off somewhere else for PE. There seemed to be no stability, but I always felt comfortable with John Clegg.
As a form master, he gave me great encouragement. At first I was a bit lazy and he realised I was holding back, so he started to push me. By the end of the year I was winning prizes. Any time that I wanted to try something new, I'd go and speak with him first and he'd say, "Yes, that should be fun - have a go!" He never put me down.
My reports used to say: "Ainsley has the ability to do what he wants to do, but he needs to concentrate more." I still have lapses of concentration when I'm cooking on TV. I can be going along OK and suddenly think, "What am I going to put in there now?", but I can always joke my way out of it.
I think that John Clegg encouraged me in this, because we shared the same sense of humour. He once said to me: "You're the only person who can make me laugh, even when I'm in a rage. You only have to do your Sammy Davis Jnr impersonation, and I break up."
Looking back, I think that's what gave me the confidence to realise that I could bring people out of themselves by using humour, and it certainly stood me in good stead when I was working as a stand-up comic. By then I was a chef at the Westbury Hotel, and as soon as I'd done the evening service I'd run down to the Comedy Store, change into another outfit and go straight on stage to become one of the Calypso Twins!
If I hadn't been a chef, I might have been a dancer. I did some professional dancing at the Barbican but, to be honest, I thought it was a little bit posey.
As soon as I left school I travelled round France for a while, which really opened my eyes to a completely different way of cooking.
When I got back home I went to see a careers officer, and when I told her I wanted to be a chef she said: "Oh, you don't need to do that - you're quite a bright boy." Funnily enough, I don't remember her name!
Ainsley Harriott regularly appears on 'Ready Steady Cook' and presents 'Can't Cook Won't Cook'. His latest series, 'Meals in Minutes', appears on BBC2 early next year. He was talking to Trish Walters