A gentle English teacher was this budding thespian and Teddy Boy's lifelong mentor.
I was deliriously happy at every stage of my education, from kindergarten to Cambridge. There is just something about me that has always wanted to learn. So at school, though I wasn't exceptionally clever, I made up for it by being a terrifically willing swot.
I had rheumatic fever at the age of 10 and staying in bed for a year put me behind educationally. I completed my 11-plus by post and, having done only middlingly well, I was accepted into the B stream of the local grammar only after being interviewed by the headmaster. So I was always determined to work my way up and to justify the school's faith in me.
As in all schools, Leyton County High for Boys had its yob element and I don't think they had a clue what to make of me. I was always in school plays, which was for sissies - plus I spoke with a posh accent, though heaven knows how. I was the only son of much-adored, lower-middle-class Cockney parents. But I suppose I'd picked up the accent from constantly watching the BBC during my illness.
But confusingly for the yobs, I was also a Teddy Boy with beetle crusher shoes, drape jackets and a Tony Curtis hair do. They couldn't work out the contradiction between how I looked and how I sounded. They'd say: "'Ere Derek, where d'ya get yer 'air done?"
One person who really did "get me" at Leyton was Bobby Brown, my English teacher. There were many good teachers at the school but he really changed my life and put me on the road that I have been travelling ever since.
Bobby, as he became to me later when we were friends, was in his late 20s, very tall and a bear of a man. He was freckly and slightly chinless, so not much of a looker. But he had this extraordinary gentleness and intensity, and he was a theatre fanatic with an encyclopaedic knowledge.
I think he saw in me a kindred spirit as well as someone who could act. He set about not just nurturing my talent but displaying it too. He produced and directed all the school productions and there was always a plum role there for me.
At 17, he cast me as Hamlet in an all-boys production that we took to the Edinburgh Festival. We received such amazing critical acclaim that I found myself profiled in The Observer and wooed by the Royal Court Theatre. And so I went up to Cambridge to read history as planned, knowing that I already had one foot on the ladder thanks to him.
Bobby was never an actor himself, but he knew good acting - and the reverse - when he saw it. As a teenager, I was always able to tear a passion to tatters and scream and shout and think I was being frightfully emotional. But he'd say: "Whoa, that isn't how you do it." He was the first person to teach me that in acting, as in life, less is often more.
Throughout my career he came to all of my plays, often sending me withering criticisms afterwards. But I never minded because I knew that his notes came from a constructive place, and if he praised me it was always entirely genuine.
Now in his mid-80s, he's living in a home and not well enough to come to the theatre. He saw me last when I was in Don Carlos at London's Gielgud Theatre two years ago. We went for our usual lunch and I took the opportunity to thank him for all that he had done for me over the years. Bobby bowed his big head and heard me out with his usual humility, love and gratitude.
Others who went to Leyton County might have different recollections. In general terms, Bobby wasn't especially suited to the job. He always had discipline problems in class, perhaps his gentleness got in the way. But to my mind there was no finer teacher. He understood that you can crush as well as nurture young people and he was never guilty of the former.
He left the profession in his 30s and got a job at the British Film Institute, which was much more up his street. But I cannot help thinking there could have been other potential young actors who would have blossomed in his care. What a loss for them, I think, when I have so much to thank him for.
Sir Derek Jacobi plays the part of Grandfather in a new version of The Old Curiosity Shop by Charles Dickens, broadcast on ITV1 on Christmas Day. He was talking to Daphne Lockyer.