If cinemagoers spot a woman in dark glasses creeping into a performance of the new St Trinian’s film, it might just be Vicky Tuck, principal of Cheltenham Ladies’ College. She is keen to see the film, which follows the fortunes of a former Cheltenham lady at the notorious girls’ school.

Cheltenham could not be more different from the fictional anarchy of St Trinian’s. It is the quintessential English girls’ school, with a history stretching back more than 150 years. Mrs Tuck, 55, is proud of that heritage, but has moved the school on.

Speaking in her first interview since becoming president of the Girls’ Schools Association, she says teachers in private schools are wrong to be “dewy-eyed” about old-fashioned education.

Before starting at Cheltenham in 1996, the mother of two was the deputy head of City of London School for Girls and PGCE course director at London University’s Institute of Education.

Mrs Tuck does not subscribe to the plan of other independent heads to develop a new national curriculum based on traditional subjects. And she fears that public-benefit tests, which independent schools will have to face to retain their charitable status, could have a negative impact.

Last year prep school leaders said that “trendy lessons” on climate change and multiculturalism were having a disastrous effect.

“I’m wary of this notion of getting back to basics,” says Mrs Tuck. “The basics of the 1950s are not the same as the basics of today. People want to know about multiculturalism and the environment. What’s wrong with learning about those things?

“It’s a complicated and fast-moving world. I don’t advocate a return to the past, which was not as glorious as people like to think.”

Further proof of her progressive stance is demonstrated by the school’s support for an academy planned by the diocese of Gloucester - although Mrs Tuck is quick to stress that not all private schools should feel pressured into supporting the initiative.

Mrs Tuck has grabbed headlines by saying that boarding schools offer children a refuge from “helicopter parents” who hover over their offspring putting pressure on them to succeed.

Cheltenham Ladies’ College, where the school motto is “May she grow in heavenly light” and which boasts super-banker Nicola Horlick and actress Kristin Scott Thomas among its former pupils, is one of the most expensive schools in the country. Boarding fees range up to pound;27,630 a year.

Mrs Tuck is unapologetic about this. “We aren’t embarrassed by paying a decent sum for a nice house, a nice jacket or a nice engagement ring,” she said. “Yet if you decide to spend your earnings on the most valuable thing you can - to give your children an education - you are damned for doing so,” she once said.

Independent schools will come under increasing scrutiny this year with the publication of guidance from the Charity Commission on the public benefit tests.

Private schools will be expected to show they are helping children from poor backgrounds whose parents cannot afford to educate their children privately.

Mrs Tuck told The TES that schools need to be careful that they do not damage their own pupils’ education by trying to too hard to appease the Charity Commission.

“We have to be careful not to dilute what we offer our own girls because that’s what our success depends on,” she says.