I have a lot of fond memories of school and a lot of it was sheer hell. Because I was fairly bright and got good marks in exams, I was labelled as a swot, which I absolutely hated.

I was very weak physically, so I couldn’t batter the shit out of all those people who picked on me. The only way I could resolve it was by being deliberately mischievous and cheeky to teachers, to make my contemporaries like me.

There were some bricklayers doing some alterations and during the lunch period we got together and bricked up the headmaster’s office. He wasn’t inside it but he couldn’t get in. I think I had detentions for about a year, which enabled me to pass French O-level.

I went to Garw Grammar School. It is Welsh for rough - it was referring to the terrain rather than the people - but there were a lot of scraps. It had a wide catchment area and there were all sorts of rivalries, based on which village you came from, which town and even which side of the street.

The other way I counteracted the namby-pamby weak link was to befriend all the toughs. I almost had a sort of bodyguard, although it cost me a fortune in fags. I became head prefect because I got into Oxford - they virtually had no choice. But after a month I was suspended for running a protection racket and allowing the form 1 and 2 kids to smoke in the toilets.

I did very well in most subjects, but always did atrociously in art, so my position in the form was not always first. I don’t think I ever got more than 15 per cent in art, which caused my average to plummet.

I enjoyed very little of the work. I wouldn’t describe myself as an academic at all: I just learnt what I had to do. My fondness for school came from it being a mixed school and being able to have sexual adventures early on.

Cyril Matthews was the physics teacher. He was very, very clever. He used to be a rugby player - a centre - and he was a tough, short person; one of those really aggressive, short, violent people.

He only taught in the senior school, from 14 upwards, and the first day I went into his class he caught hold of me, put me over a physics bench and battered the fuck out of me. He said: “This is what you get if you misbehave in my class.” It was really petrifying.

It was a challenge: “I’m not going to let that fucker push me around.” He once gave me one to the chin, a virtual knock-out blow. I had a bruise for weeks. His nickname was Killer Matthews. Everybody tried to do really well in his class. He is also the reason I ended up with a physics degree from Oxford.

He would never hold back on me - he would look for reasons to tell me off. If I smiled at something he would be on my case. But he could switch all that off. He dealt with the two sides of my character, the bright side and the mischievous side, totally independently of each other.

He became quite friendly over the years and by the time I left the school we were very close friends. He gave me a lot of private tuition. It would not have occurred to me for a second to do a physics degree without his influence. In a way it was a pity, because I had no interest in it at all. Whenever I went home in the vacations I would go to school and see him.

That sort of thing wouldn’t be allowed today, of course. I can see the advantage of corporal punishment, but it is wrong for anyone to hit a child. I can’t approve of it, even though it works.

Howard Marks, author and former drug smuggler, will be at the Theakstons Old Peculier Crime Writing Festival in Harrogate from 21-24 July, www.harrogate-festival.org.uk. His latest book, `Sympathy For the Devil’, is published by Vintage at pound;6.99. He was talking to Nick Morrison.