Bonkbuster queen returns

As soon as the door to the Royal Suite at London's plush Mandarin Oriental Hotel opens, Jilly Cooper pulls me inside and off on a gleeful tour of the palatial rooms.

"Come on!" she exclaims, like a child in a very luxurious sweet shop.

We jointly 'Ooh!' over the size of the bed ("Did you bounce on it?" I ask. "No, but my grandchildren did," she tells me) - not to mention the private dining room, enormous bathroom and multiple wine fridges.

The suite is a "lovely" upgrade, says Cooper, explaining that Channel 4 are making a documentary about the hotel and filmed the lavish launch party for her new book Mount! here (guests included a Polo-munching rescued grey stallion).

She was also pictured at the event with the three men she now admits she based her lovable rogue Rupert Campbell-Black on: Andrew Parker Bowles, Rupert Lycett-Green and the Earl of Suffolk.

"When I moved to Gloucestershire, I met three very glamorous men, who were beautiful and quite aristocratic and grand, and they all influenced him," says the writer, who swapped London for the countryside back in the Eighties. "They behaved very well, they didn't do any of Rupert's naughty things, but it was their charm and charisma that impressed me."

The 'queen of the bonkbuster' is an extremely youthful 79.

Elegant in a cream silk shirt, she oozes joie de vivre, and seemingly manages to find the positive in whatever life throws at her - whether it's the minor stroke she had in 2010, which gave her the opportunity to admire the seagulls during her hospital stay, or her late husband's battle with Parkinson's, which inspired the "wonderful" carer Gala in her latest book.

The 10th in her bestselling series of Rutshire Chronicles, which began in 1985 with Riders, Mount! is a deliciously escapist romp, following horse trainer and breeder Rupert's bid for Love Rat to win the title of 'Leading Sire', the stallion whose progeny win most races. There's rivalry, sabotage, and the action culminates at the Dubai World Cup.

Cooper's still worried about what she left out, however. "It's an awfully embarrassing thing," she says with a giggle. "I've got about 55 notebooks all round the house, saying, 'Mount! Crucial to add!', and I haven't added it at all."

She still handwrites, or types her manuscripts on an old typewriter, and each book can undergo several drafts before she's happy with it.

"I just write all day, and sometimes all night, and then Saturday and Sunday. I just write," she explains, acknowledging that the habit sometimes takes over.

"I love my grandchildren, but I'm not a terribly good granny, I don't have them for days on end. I'm not very good with babies. I've got two copies of The Good Granny Guide, which I haven't opened!

"Also, I think it's very immoral of your generation to have children and just expect grandmothers to look after them," she adds. "They're babysitters."

Cooper began her career as a journalist at The Middlesex Independent in Brentford. After a chance meeting at a dinner party with the editor of The Sunday Times magazine, she was asked to write a column, and soon after moved to the Mail On Sunday, where she worked for five years.

Her first book was the non-fiction How To Stay Married in 1969.

"A publisher asked me to write it and I was absolutely knocked out - I was longing to write a book. If I'd been asked to write a book about a rhinoceros, I would have done it!"

She met her publisher husband Leo in 1945 at a party, when they were both just children.

"A girl called Louise Tate was rabbiting on about how much land her father had. Leo picked up a strawberry jelly and went wham! He hit her absolutely in the kisser," Cooper remembers. "So brilliant!"

She was 24 when they married. Cooper was left unable to conceive after an ectopic pregnancy, so they adopted Felix and Emily, who both read their mum's books.

"Felix read Riders at school, and said 'Ma!'" she recalls.

"Children actually like their parents to be earning a bit of money," she adds. "They'd much rather be bought a new game or a T-shirt than their mum say, 'No you can't have that'."

Jilly and Leo were married 52 years, until his death in 2013.

"I think marriage is an awful lot of luck," she says, taking a sip of white wine. "Can you imagine the horror, the ghastly horror, better to be in Pentonville, Broadmoor or anywhere, rather than being stuck with somebody you didn't like."

She attributes the longevity of their relationship to giggling.

"It's bed springs creaking from screaming with laughter - not from sex. Sex is wonderful of course, but I think it's finding things that amuse you, and Leo was very kind. It's lovely to have someone back at the ranch who's rooting for you."

Famous for her good-humoured sex scenes, one of the funniest in Mount! is between newly-wed 70-something racehorse owner Etta and former footballer Valent, the main love story in her previous book, Jump!

"It was heaven to write," she says of the scene, in which Etta dresses up in Ann Summers lingerie only to be spotted by a grandchild.

It's refreshing to read a romp among those with less pert bottoms, but does Cooper think sex among older people is still taboo?

"People who are 14 think you sort of stop at about 25. We're not being more prudish, it's inflicted, because you can't say anything now, can you? We're getting more and more respectable. It's a Victorian age being imposed on us."

Cooper has read E.L. James' Fifty Shades Of Grey; she's typically tongue in cheek when asked what she thinks: "Well done her. She's published by my publishers and she's sold a hundred million copies, so they can afford me..."

It didn't make her feel the need to up the raunchiness, however.

"I just carried on in my awful, decadent way. I don't think it's that difficult [to write a sex scene], but I'm so old now, I've forgotten how to do it, so I have to sort of remember," she says, laughing again.

Riders was made into a TV film, and the rights to nine of the Rutshire Chronicles have now been bought for future ITV adaptations.

Cooper has already started "messing around with characters" for her next novel too, which swaps riding boots for football studs and is cheekily called Tackle!

"I met Alex Ferguson at dinner and he was absolutely lovely - I was always a bit scared of him before. He was riveting about football - very light and funny and passionate about getting the young involved," she says, explaining the inspiration behind the theme.

Besides the action on the pitch, the plot will also see Rupert's young publicist, Dora, trying to save her local newspaper, a subject close to the writer's heart.

"She's made editor at the age of about 20. I'm passionate about local newspapers, because they are the guardians of our morality and our democracy and I think they'll all be closed down," says Cooper.

"And the things you can do... I mean, just a brown envelope across a table in the country and you can build a house anywhere you like."

• Mount! by Jilly Cooper is published in hardback by Bantam, priced £20. Available now