Mr Cooper was head of the arts department at Newlands School in Seaford. He had a very dry sense of humour and I was never entirely sure whether he was joking or not.

He had one of those faces that could say a huge amount without him actually moving it. He could have been an actor.

But he was a teacher and an extremely good one. He had a real passion for the arts in general. I was already into my acting career at that point, but he inspired me to take an interest in the visual side of what I was doing.

I remember going to museums as a kid, but I don’t remember going to art galleries. Now, though, every time I go on holiday or visit a city, I make a point of visiting the art galleries - I think that threads back to Mr Cooper.

I’m pretty sure I picked photography and art as two of my GCSE options - both of which he taught - because I wanted to avoid written coursework. That backfired massively because there’s quite a lot of written coursework for both subjects. For every painting you did or photo you took you had to write up why you did it. But I’m so glad I took both of them.

Music and tea

Mr Cooper was a very laid-back teacher. Not in the way he dressed: he was shirt and tie at all times - even in the art room, the messiest room in the school. But he’d let us play music and make tea and he’d even let me come in on lunch breaks to work. I think I made some of my best school friendships in that art room.

At one point I stole a key and would let myself in. If Mr Cooper caught me he’d ask how I got in and I’d just fib and say the door was open. I still have the key! The school is closed down now, but if I wanted to get back into that room I could.

I think he saw me in a way that other teachers didn’t. I had a bit of a tough time at school, not because I was badly behaved or that I didn’t work hard, but because I was always under the delusion that I was already pretty clever and teachers, as a rule, don’t like that.

Incredible skill

Mr Cooper gave me some hard truths. He put me in my place, but he did it without making me feel discouraged. What an incredible skill that is for a teacher. He was the one member of staff I felt I could speak to with a level of mutual respect and understanding. He treated me like an adult.

It’s difficult when you’ve been working [as an actor] since the age of 12 to go back into a school and be patronised every day, especially when you’re a teenager and you’re exploring your own ego. He wouldn’t do that. He wouldn’t patronise me.

What he encouraged in me is to want more. Whatever you’re doing, it’s great if you’re doing well, but you should always try and do better.

That’s something that’s very lacking in the film and TV industry right now. There are so many people with so much talent and yet we still seem to be seeing the same thing produced over and over again. And it’s not that we are out of ideas. It’s not that there’s no such thing as originality anymore. It’s that we are no longer trying as hard as we could be. Mr Cooper wouldn’t stand for that.

Endeavour continues Sundays at 10pm on ITV