Rupert Campbell Black is back in Jilly Cooper's 10th raunchy riding novel

At 79 years old Jilly Cooper oozes joie de vivre.

She seems to find the positive in whatever life throws at her - whether it’s the minor stroke she had in 2010, 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 Campbell Black’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. “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 grew up in Ilkley and attended Moorfield School before heading south. She 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. She met her publisher husband Leo in 1945 at a party, when they were both just children. She was 24 when they married. Cooper was left unable to conceive after an ectopic pregnancy, so they adopted Felix and Emily.

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

“I think marriage is an awful lot of luck,” she says. “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.”

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

Mount! by Jilly Cooper is published by Bantam, £20.