Most of my memories from school are sport rather than academic related. I am one of four boys and to varying degrees we are all sporty. I remember things such as the time I took nine wickets in an innings. And I remember very clearly being picked above my age group for the football team, my mum and dad coming to watch, and me being substitute and never getting on the pitch. I remember how bad that felt, and one of the rules I have always had with the football teams I coach is that if you’re picked for the squad you play.

I had a natural aptitude for maths and I remember being the first child in school to complete my times-tables. There was a little chart on the wall with our names on and you ticked the box when you had learnt your times-table. I am a very competitive individual and I remember being determined to be the first kid to complete them. Maths was always my thing.

I passed the 11-plus and went to Tudor Grange school in Solihull, which changed to being a comprehensive in my second year, and from there I went to Solihull sixth-from college. My favourite teacher was Dr Gobbett, who taught geology. My plan, aged 16, was to study geophysics at university - that’s quite a scary thought now, I can’t imagine why I ever thought that was a good idea - and the classic combination at A-level for that was maths, physics and chemistry. I didn’t enjoy chemistry, but I had a vague interest through geography in geology so I did that instead.

In some ways it seems a bit odd to pick Dr Gobbett because he only taught me for two years and I didn’t go on to do geology at university. But the reason why he is my most memorable teacher is that he took a class of pupils who had never done the subject before and enthused them. He couldn’t believe his luck that someone was paying him to transmit to children his passion for the subject. He was one of those very expansive teachers; his arms would always be waving about, and he always gave 100 per cent. He was very animated.

On field trips, he would head off up the mountain with his hammer out and his little rucksack for holding his samples. I was a reasonably fit 17-year-old and I remember climbing behind him and being absolutely exhausted as he headed off to another rocky outcrop. I can remember going to Lyme Regis and Durdle Door and getting hugely excited and inspired by what, after all, were just rocks. He was slim, with a scraggy beard: exactly what you would expect a geology professor to be. We called him the Mountain Goat.

There were only 16 or 18 people in the class and many of them, who like me were doing the subject as a bit of a filler option, went on to do it at university. He had an ability to inspire and an absolute commitment to his subject; it was what he spent his life doing. He went off on holiday to look at rocks. My family think I’m a terrible bore because I’ve maintained an interest in geology, and wherever we go I’m interested in what the rock strata is and how it came to be as it is. My children think I’m a boffin.

I went to Bath University to look at the course and realised I wasn’t up to doing such a highly technical subject as geophysics. I sat on the bus on the way home looking at the prospectus and wondering what else I could do that sounded interesting. I chose business studies. As it turned out I had found the thing that I wanted to do.

What Dr Gobbett taught me about most was passion and commitment. I have always believed that whatever you are doing, you should do to the best of your ability. My personal philosophy, and the thing I try to teach my children, is to do the things you enjoy rather than the things you think you have to do. You are much more likely to do it well if it is something you enjoy.

Businessman Justin King was talking to Harvey McGavin

The story so far

1961 Born London

1966-77 Attends Dorridge primary school then Tudor Grange school, Solihull

1977 Solihull sixth-form college

1979 Business studies at Bath University

1983-89 Joins the Mars graduate trainee programme

1989 Moves to Pepsi Cola International

1990 Responsible for UK launch of HAagen-Dazs ice-cream

1993 Joins Asda. Becomes managing director of hypermarkets

2001 Appointed food director of Marks Spencer

2004 Becomes chief executive of Sainsbury’s

2005 Sainsbury’s launches Active Kids voucher scheme for sports equipment for schools