Passing on PG tips

She is only 25 but she's already had her big break, directing Caryl Churchill's Top Girls last summer at Battersea Arts Centre, followed swiftly by the chance to direct the long-running hit Art. She's won an award for young directors and turns up in those lists of hot young hopefuls to watch. Now she is the youngest artistic director in the country, at Southwark Playhouse, where she was appointed in January. The first play she has directed there herself opens next week.

Phew. If the rise and rise of one so young is a dizzying prospect, pause to note that one of her best moves was to approach a man 40 years her senior, the distinguished director and playwright Peter Gill, founder director of the Riverside Studios and the National Theatre Studio.

In 1999, Gill was to direct David Mamet's Speed the Plow in the West End, starring Mark Strong, an actor Sharrock admires hugely, and Patrick Marber in his stage debut. She offered her services, gratis, as an assistant director.

"I nearly fell off my chair when he phoned me up and suggested we meet," she recalls. "She was bright, very clued up about things relevant to that production," he says. A colleague recommended her and he noted that she had been a member of Anna Scher Children's Theatre for 10 years, then worked at both the NT Studio and the Market Theatre in Johannesburg in her gap year between St Paul's and Oxford.

Although she was president of the university dramatic society, she left a year early, eager to move on. All this helped convince him that she was not just another Oxbridge-only wannabe. He took her on. "Thea was very, very good at helping - being there with you, talking things through, being one step ahead, making a good relationship with the actors," he says.

Sharrock found him to be a brilliant teacher and a very generous director.

"He said to me very early on, 'Casting is all - 80 per cent of the work is done if you get that right', and, by God, was he right. The most important thing I learnt in rehearsals was to admit that you don't always have instant answers to everything. That honesty is more important than pretending. Actors love working with him because he really cares about the people and the process.

"We are both interested in the details that say a lot about a person, and he is brilliant at piecing people together. He is not interested in spectacle, in making a big splash; he is interested in quality work." She also admires him for sticking to his guns. "He is not interested in the bullshit and I think that's wonderful."

He has made her unafraid to ask the most basic questions, she says, citing this as the main reason they have become friends. When the post at Southwark - of which Gill is coincidentally a patron - became available, it was to him she turned for advice. When it came to choosing a programme for the Playhouse, she realised, however, that she had never read any of his work. "I went to the NT bookshop and bought everything they had by him and I thought - she takes a sharp intake of breath - 'This is so me.'"

So next week will see a double-first: Sharrock's debut production will be Gill's earliest play, written when he was the same age as she is now. The Sleepers Den, set in the writer's native Cardiff, is a study of poverty in the 1950s, centred on a few days in the life of three generations of one family. "It just felt right," says Sharrock. "Nothing much happens in Sleepers Den but the first time you read it you know these characters exist. It doesn't seem dated, because the writing is so good, given that he was so young when he wrote it. The strength of all his plays is the dialogue."

Gill comments that it is a sign of Sharrock's boldness that she has chosen it. "It's a different kind of calling card. There are not many young artistic directors who would schedule it at the moment." Although she has spoken to him on a daily basis about the play during rehearsals, she is more nervous at the thought of him in the audience than of anyone else. He expects the production to be, like its director, very fresh.