If I can credit any teacher with changing my life, it was Peter Nixon. It seemed as if he looked at me and understood from the word go that acting was what made me tick. Looking back, I probably wanted to be an actor from the age of seven, when he started casting me in plays at Lochinver House School, an independent all boys’ prep school in Potters Bar, Hertfordshire.

At that time, Lochinver was renowned for its plays. One year we put on a production of Treasure Island and Mr Nixon cast me in the plum role of Long John Silver. Another year, I was Fagin in Oliver!

Perhaps because of my background, it took me longer than Mr Nixon to realise acting was my calling. My parents were loving, hard-working people who’d come to England from County Mayo in Ireland in the Sixties. My dad was a builder. So saying I’d like to be an actor would have been like declaring my intention to be an astronaut or president of the USA.

On top of this, my parents’ dream was to give my two younger sisters and myself the kind of education they hadn’t had. They hoped we’d become successful professionals. So after Lochinver and then Haileybury, a boarding school in Hertfordshire, I went to Cambridge to study law.

But from week one, I knew I’d never make a lawyer. I got involved in drama productions and started mixing with people who declared quite openly that their career plan was to become an actor. And I started thinking: “I could do that”. So after Cambridge I went to RADA. But I was 26 before I finally started working in the career that Mr Nixon had probably always known would be my calling.

He taught me from the age of seven to 13 and got me interested in theatre, film and literature, opening up a creative world at an age when I was willing to absorb it like a sponge.

His subjects were the conventional ones - history and English. But there was nothing conventional in his approach. It was not unusual for him to arrive in class with a large screen and projector that he’d set up to show us - a bunch of eight-year-olds - Sergei Einstein’s 1925 movie The Battleship Potemkin or any one of a number of silent classics.

He never patronised us or thought that being young was an obstacle to us appreciating these greats. Afterwards we’d talk about what we’d seen and he’d listen to our views as though our insights were the most invaluable contributions he’d ever heard.

Mr Nixon gave you respect but expected you to be worthy of it. He wasn’t a soft touch and if you let him down he’d let you know. But mostly my recollections are of a teacher with a quietly infectious passion about the subjects he taught and about teaching itself.

He ran a film club at Lochinver and we would create our own masterpieces on cine cameras. One year, we won the title of Young Film Makers of The Year on Screen Test, the BBC children’s show.

We worked for nine months on an animation film called Dougie, creating the whole thing out of pink Plasticine, painstakingly completing one or two frames a week until we had a film that was three minutes and 17 seconds long. Even now, I’m as proud of that film as anything I have done in my career.

When I left Lochinver, I didn’t expect to see Mr Nixon again. But a few years ago I was in a Noel Coward play at London’s Savoy Theatre and he was in the audience. Afterwards, he came backstage and we chatted about old times. It was terrific, if a little weird, because the last time I’d seen him I was 13. I was able to thank him and we talked as two grown men.

Stephen Mangan has appeared in a raft of TV comedy roles including Green Wing and Never Better. He was talking to Daphne Lockyer.