File photo: Jilly Cooper (right) and daughter Emily arrive for the Cartier Queen's Cup at Guards Polo Club, Windsor. Picture: AP

Tinder. Endless champagne. Oodles of young men. A riotous encounter with Jilly Cooper who proves you can be sexy at 80. By Jan Moir

Deep in a luscious fold of the Gloucestershire countryside, an octogenarian widow celebrates an important birthday.

What is on the agenda, pray tell? Gift-wrapped lavender bath salts, box pleats, an egg on toast and an early night?

Not if that woman is Jilly Cooper, the celebrated author of horsey bonkbusters who is growing old as disgracefully as she can possibly manage. "Oh, my birthday was heaven, I was drunk for a fortnight," cries Jilly before correcting herself.

"When I say drunk, I don’t really mean drunk, I mean full of wine."

Is there a difference?

"Yes my darling, because I have given up vodka in a pathetic attempt to be slightly more sober," she says.

Today, she drinks only champagne or wine — so virtuous! — and tries to limit her intake to three glasses a night, which makes her practically a saint compared to the Jilly of old.

She once wrote a guide to giving dinner parties, which advised getting all the guests so drunk beforehand that they forgot about the food afterwards.

When she turned 80 at the end of last month, the television host Richard Madeley rang up first thing to wish her a happy birthday ("wasn’t that divine?"), and her gifts included an original Garfield cartoon, a star named after her, two trees ("I love getting trees"), three carp for her pond because the other ones died, and a "beautiful pink jacket", which is quite funny because Jilly once wrote disparagingly of women who "wear shocking pink in the country".

"And now I am that woman, and I love it."

The celebrations involved lunches, parties and a delegation of players from her local football team, Forest Green Rovers.

Cooper’s next book is set in the world of football and she has become a keen supporter and friend of the Rovers, who seem to have a disproportionate number of handsome hunks among their team. Typical!

"To have one’s drawing room full of gorgeous men on one’s 80th birthday is quite an achievement, don’t you think, mmm? So lovely! I really enjoyed being 80. In fact, I want to be 80 every day for the next 20 years."

Another recent milestone has found her becoming proficient in the use of the dating site Tinder.

"Swipe left and right for like and not like. I loved it!" she says "I also tried speed dating, which was new to me, where you have to decide if you like a man in four minutes. In my day it was the four-minute mile, now it is the four-minute male."

I barely notice the first of her trademark puntastic jokes being slipped into the conversation, as I am still reeling at the news: Jilly Cooper is on Tinder.

"Not really," she protests. "Only for research purposes because I want people to do it in my next book. They are all going to flick away like mad."

Way back when, Cooper was the original Bridget Jones, writing a popular newspaper column about her love life that ran from 1969 to the mid-Eighties. She went on to write 46 books, selling untold millions of copies, with the most famous being her ten horsey novels known as the Rutshire Chronicles.

These include the best-sellers Riders, Rivals, and The Man Who Made Husbands Jealous, all of which feature her hero, Rupert Campbell-Black — the "handsomest man in England" and someone who is "ruled by the privates".

He is famously inspired, in part, by Jilly’s great friend, Andrew Parker Bowles, along with her other pals Rupert Lycett-Green and The Earl of Suffolk.

Please note that Jilly doesn’t believe that posh people are necessarily better in bed, only that they probably are because they have had more practice.

"There will always be some wizard aristocrats in bed and some lousy ones. What I have always said is that posh people are more promiscuous. They are more demanding and used to getting what they want. Droit du seigneur and all that."

No wonder Jilly had a Spitting Image puppet that bounced around shouting "Sex! Sex! Sex!" all the time. Her most popular books were set in the freewheeling period that was post-Sixties and pre-Aids, when lovers were carefree, men were men and horses were horses.

Generations of schoolgirls first learned about sex through the (surprisingly wholesome) dirty bits in her books.

For in Jilly’s fictional heartland of fetlocks and fornication, men made love like "an express train going into a tunnel", nipples were "strafed" and the sex was invariably redeeming in some marvellously bucolic way.

Held in high affection by her millions of fans, Cooper has trotted through the gymkhana of British public life for almost half a century, always wearing her winners’ rosettes with a certain dimpled modesty.

"I read my entry in Who’s Who the other day. They sent it to me to be corrected. And I thought, gosh, that is not bad," she says. "Not bad at all."

We meet at her home near Stroud, a beautiful 14th-century chantry with views down the valley, wisteria stems arching around the front door, and the flagstones within grooved by the reverential tread of monks.

I last came here 18 years ago to interview Jilly when she had just published her 36th book, the novel, Score! "Oh, it got terrible reviews, do you remember?" she says. "I had dedicated it to my housekeeper, and one reviewer said that it was so bad I should have got her to write it. Hysterical."

Today, there is a wisp of melancholy in the air; a sense of the years peeling back, of more endings than beginnings. "I have to accept now that I am in the winter of my life," she says.

Writing never comes easily to Cooper, but working on her 2017 novel Mount! was a particular torture. She could never remember what she had written the day before, and had to re-read chapters every morning to remind herself of the plot.

"I worry about dementia and constantly ask everyone if I am going off my head. I am always scurrying in and out of rooms trying to remember why I went in there in the first place," she says. There has been a physical deceleration, too.

"I wish I was more mobile, but I have become dependent on bannisters and bathroom rails."

Where once upon a time there were an obstacle course of sleeping dogs to negotiate, today there is only one, a rescue greyhound called Bluebell. A stair lift is attached to the stone staircase, and the absence of her husband Leo Cooper, who died in 2013 after suffering from Parkinson’s disease, is marked.

The couple were together for more than 50 years although they each had an affair; hers during the early days of their marriage, his a six-year dalliance that was made public in 1990.

"It was like a crucifixion," she says, but the marriage survived. Unable to have children together, the couple adopted Felix — now aged 48 — and Emily, 45.

"I absolutely love them, they are a huge comfort and lots of fun," she says. Jilly now has five grandchildren, Jago, Lysander, Acer, Scarlett and Sienna, but is too absent-minded to babysit.

"I am not a very good granny. I love my grandchildren, but they don’t get left with me because I wander off and forget them."

Leo spent the last two years of his life in a ground-floor room here, slowly slipping away from the world, but still clinging to his passions. "Leo loved Posh Spice, he loved Fiona Bruce and he loved Kay Burley," says Jilly.

"One of his carers pinned up a picture of Kay at the end of his bed, and that cheered him up when he was very ill. Since he died, I haven’t cried. I don’t know why."

When I first came here all those years ago, her office was in a stone gazebo in a tranquil corner of the garden, but that is now completely silted up with the detritus of her work, or what she calls her "crud, paper and muck".

She turned a room upstairs into the same state and is now in the process of wrecking Leo’s old office, too, because she simply cannot bear to tidy up or throw anything away.

Her entire home is like some crazy warehouse crammed to the rafters with tapestries, cushions, ornaments and paintings, all depicting horses and puppies, ready to stock the shelves of some nightmarish Cotswolds knick-knack shop.

"I think I have anal retention. Or perhaps, it is complete laziness," she shrugs.

In her jeans and crisp blouse, with her mophead hair as thick and shaggy as ever, Jilly is still as pretty as a milkmaid, but perhaps a little frailer than before.

She had a stroke in 2010 and a hip operation two years ago which "didn’t go quite right" and is still a cause of discomfort.

In 2016, she fell out of a tree when trying to rescue a ladybird in her garden and badly cut her leg. It became infected, necessitating regular visits from the district nurse and it took months to heal. "A bore."

Meanwhile, she takes drops for her glaucoma and so many pills that "I rattle like a tube of Smarties". These include vitamins, pills for blood pressure, statins, aspirins and Berocca.

"I once had an ectopic pregnancy — that was my only flicker of fertility — which stopped me from having babies, but I am very healthy really. The only thing that does quite scare me is the thought of a stroke again. When I get tense, I am terrified I am going to have another stroke, so I deep breathe and things like that."

She worries about her weight, her weakness for cheese and what she calls her "marshmallow thighs and elderly spread".

Heaven knows why, for she is still as tiny as a field mouse, one that quite possibly hasn’t eaten a single carb since my last visit. And yes, she is always charming and determinedly jaunty, but what I like about Jilly is that she is not quite as fluffy and jolly hockey sticks as you might imagine. "One of my weaknesses is being two-faced.

"I can be absolutely beastly to people behind their backs," is how she puts it. "He’s really up himself, isn’t he?" she says suddenly, of a mutual acquaintance.

"A friend met her at a dinner party, God, she’s so stupid," she says of another.

That surprising dash of lemon curdle in her cosy, clotted cream persona? It makes her more, not less, likeable. She no longer grieves every day for her husband — "we had 13 years to say goodbye" — but is still occasionally capsized by memories.

"Well, I still miss him terribly. I get depressed when I hear music that reminds me of Leo. Or remember private jokes we shared. And I tell you something else that is awful at my age. You look around your house and you see lovely photographs of people, but practically everyone is dead."

Does she think about death?

"All the time. I couldn’t get another dog, for a start. I don’t fear dying, unless I was in a wood and someone was running after me with a knife. I hope that when I die I will see Leo and my family again, but I can’t bank on it."

They married when she was 24 and on their ruby wedding anniversary, Jilly wrote that "I couldn’t have had a dearer, kinder, more stalwart captain of my ship". They had a party here to celebrate their golden anniversary and, poignantly, the ribbons she tied around the statues in the garden are still there today, fluttering in the spring breeze.

However, hang on to your hollyhocks because the sun has not set over Rutshire just yet. Sometimes, Jilly Cooper longs for the chance of romance and to fall in love again, but despite the parties and the Tinder and the footballers and the diet, she is not looking. Not really.

"I think I am a bit old to subject myself to somebody, quite honestly. I have to take my teeth out at night, and that wouldn’t be much fun for anyone.

"Darling, they would have to turn the light off and who wants that? Anyway, I don’t miss sex any more, I just miss Leo. Now. Shall we have a drink?"

Somewhere inside the heavenly chantry, delicious snacks are produced, a cork is popped and as the evening shadows lengthen across the honey Cotswold stone, valiant Jilly toasts the remains of the day with a small glass of champagne. "Why not?" she says. Why not, indeed.

* Mount! by Jilly Cooper is out now in paperback