Jilly Cooper is nearly 80 – but she’s still the undisputed Queen of the Bonkbuster

In Mount!, Campbell-Black, now 60, is still a bounder but tamed by marriage to Taggie. “She adores him, which psychologically makes Rupert feel he’s not such a bounder after all.”

I say it’s refreshing the older characters in Mount! have a fulfilling romantic life. “Everybody, given the chance and an attractive partner, would have sex at any age,” Cooper insists. It’s not just the humans getting frisky. Researching the new book, Cooper fell in love with the “breeding side of racing”. And some of the detail in the book is jaw-dropping. She encountered stallions who only fancy grey mares (a white sheet is put over coloured mares for mating). Another would only perform if the vet held his hoof.

Arguably we adore Cooper’s escapist romps because they evoke a lost England of cricket on the village green and endless G & Ts. She’s touched they’ve named a race at Newbury after Mount! “And a lovely man has named a racehorse after Rupert Campbell-Black. A two-year-old, it’s just been gelded. Poor Rupert’s just been gelded!” she hoots.

Marcus Gilbert played Rupert Campbell-Black in Riders in 1993

Cooper is as funny as you’d hope and enjoys being mischievous through her characters. She loathes charity fundraisers – “Rupert says: ‘If I see another crone with a bucket I will kick her teeth in!’” – and says a headmistress recently wrote to her asking for £150,000 to improve the girls’ dining room. “A dining room,” she marvels in Lady Bracknell-esque tones.

Another Cooper target is the worried well. “I’m going off piste now but I do worry about this thing of how you have to have counselling for the menopause. I just got on with it.” In fact, she insists women are stronger than men now. “They cry all the time men on TV, don’t they? They’re in a very bad state.”

She describes herself as an entertainer but Cooper, who was awarded an OBE for services to literature in 2004, is better read than she lets on. “Darling Walter Scott” is her hero because he “wrote for the general amusement, which is not a bad thing to say, is it?”

Cooper was bound for Oxford but an epic hangover ruined her interview. She ended up at typing college. Later she was sacked from 22 jobs before moving into publishing. She famously landed a newspaper column (the forerunner of Helen Fielding’s Bridget Jones) by impressing the editor at a dinner party.

She wrote Riders in her 40s when she and her husband Leo first moved to the country after losing all their money. It rescued their fortunes. Adapted for TV in 1993, it attracted 15 million viewers. She thinks the bonkbuster will survive: “People like reading about rich, glamorous people doing naughty things.” Though she jokes her oeuvre is now “old-boiler lit” rather than chick lit. Her next novel, Tackle, will be set in the world of football. She supports her local team, Forest Green Rovers, which she says proudly is “the only vegan club the world”.

Mount! took her six years to write and Leo, who had Parkinson’s for 13 years, died three years ago. Several of the characters in the book are based on carers who looked after them. “God, they were wonderful, they were such friends. It’s so brave because they come over from South Africa or Zimbabwe and send their money back home. It must be frightening looking after a slightly crazy old lady in a big house – like Jane Eyre, really – but they’re just brilliant.”

She says with relish that her grandchildren go round saying: “Poor Granny’s got AlkaSeltzer.” “I think I have, too.” I doubt it. That mind is as sharp as ever. Her 80th birthday is two days before the paperback launch of Mount!, “so I might just go to bed,” she demurs. Nonsense, Jilly, there’s far too much to celebrate.

Mount! by Jilly Cooper is available for £15.80 (normally £20) including p&p from the RT Bookshop