MARY Berry gave away no secrets about who wins The Great British Bake Off when she visited Oxford yesterday.

But she did reveal her secret to staying slim while tasting the hundreds of cakes as a judge and presenter on the prime-time TV show.

The 78-year-old grandmother from Buckinghamshire was in Oxford talking to fans and friends at The Fabulous Oxford Baking Competition in Summertown.

Asked how she stays so slim when she eats cake all day, she answered: “Soup.”

She said she discovered that soup helped control her weight when she started eating it a lot after her son William was killed in a car crash at the age of 19 in 1989.

She said: “Every day I have soup, which is only about 175 calories and that is it.”

But she added: “I do taste everything. Because the contestants have made it, and because their mothers and fathers and brothers and daughters are watching me eat their cake.” The Great British Bake Off, which draws in six million viewers, sees 13 contestants fight it out to win the competition.

This week’s quarter-final ended with Didcot grandmother Christine Wallace being sent home by the two judges.

Mrs Berry said: “We were awfully sad to see her go, but we were totally fair.”

Mrs Berry accepted the invitation to Oxford to help raise money for Stroud Court Community Trust, a Gloucestershire-based autism charity which originally had links with the city.

She signed copies of her books and gave a talk to the 95 who attended.

The competition raised around £5,000 towards a £500,000 fundraising effort to revamp one of the buildings at the Gloucestershire care home.

The competition’s host was the sister of one of the care home residents, Jo Lewis, who held the event in her Woodstock Road home.

Mrs Lewis said: “It’s been amazing, mainly because Mary has given so much of her time. She is incredible, she is just as she is on telly.”