They say that a good teacher shapes lives. Well, Elizabeth Sacre, my A-level theatre studies teacher, certainly shaped mine. Without her, I doubt I would be an actress today. She entered my life at a crucial time.

At 16, I was a shy, unhappy teenager. I was at St George’s School in Ascot, having moved from Dublin with my family two years earlier. It is the same school that Princesses Beatrice and Euge-nie have since attended, so it was pretty posh. And there was I, with my strong Irish accent, sticking out like a sore thumb. On top of this, my parents were going through a divorce and my teenage hormones were raging.

There was a huge amount happening in my world that I could not comprehend and I was pretty cross with everything. Enter Miss Sacre. My first memory of her was at an open evening where teachers pitched for A-level students.

She was new to the school and got up to sell her subject. She was in her late twenties, and in her glorious Wigan accent spoke about “the adventure of learning”.

There was so much passion and focused energy in her that my mum and I instantly turned to each other and said: “We’re signing up for that. Now.”

Until that point I had no clue what I might do. I was quite academic, good especially at modern languages but, at home, according to my mother and grandmother, I was also a total drama queen.

At school I loved watching other people on stage - “the tits and teeth brigade” as I thought of them, but I was too shy to get up in public. Liz Sacre, though, was having none of it. She cast me immediately as Grumio, the fool in Taming of the Shrew and told me to “play it as Irish as you want”. I loved every minute and was completely hooked.

As cliched as it will sound, acting gave me the sense of belonging that had been missing from my life. Over the years I have tried to analyse what made Miss Sacre so special. For a start, she had a way of making great drama - Shakespeare, Chekov - accessible. She brought everything down to whatever level you were at and made it completely tangible and relevant. When we did Miss Julie, the Strindberg play, I remember her saying: “Now listen to me.

At this point Miss Julie has her period, she is being treated hideously by everybody and she’s absolutely furious!”

She handed me her keys and said: “Right - you’re Miss Julie, do what you want with them.” I hurled them against the wall and knocked a lump of plaster out. Miss Sacre whooped for joy. Even now when I’m trying to find anger in a character like DCI Connor - the quietly fuming sort of character I play in Trial and Retribution - I remember the Miss Julie incident and use it.

Miss Sacre’s special gift, I suppose, was her ability to channel negative teenage angst and make it positive. In a world where teenagers are told to “shut up” or “stop it”, she encouraged the reverse. Like all great teachers she peeled back your eyes and showed you what was going on outside your field of vision. She was the first person who made me realise I could make a living from acting, and coming from a background where people made money from being entrepreneurs and business people, that was a revelation.

In my final year at school she helped me prepare for my audition at Bristol Old Vic and gave up hours to help me. She believed in me and wanted to launch me into a big arena. After I was accepted she came to a couple of productions and we stayed in touch for a while. The kind of education I want for my children is the kind Miss Sacre gave to me. It is based on the idea that you should try everything, fear nothing, dare to be different Victoria Smurfit, 32, has starred in a host of TV dramas, including North Square and Ballykissangel. In 2003 she first took the lead as DCI Roisin Connor in Trial and Retribution. The ITVseries concludes on February 11 and 12. Victoria was talking to Daphne Lockyer