The writer Jilly Cooper, who has died aged 88, was a Georgian at heart, with all the 18th century’s preference for country above city, reason above passion, and mutual pleasure above sexual sufferance. Many of her bonkbusters were based in her fictional counties of Rutshire and Larkshire, where upper and middling natives pursued land, sports, profitable businesses, and each other, with lust and gusto, as in the works of Henry Fielding.

The novels were robust, and full of comic observation – she had a caricaturist’s eye for telling contrasts of detail, a handsome sleek horse next to a shaggy-shanked pony. They sold and sold, around 11 million copies in the UK.

The journalist Caitlin Moran once suggested that Riders (1985), Cooper’s first hit, was “written by someone ablaze with desire”, and must have been stimulated by an affair. Cooper replied: “I just fell in love with the countryside, that was what made me come alive. I was having an affair with the whole of the Cotswolds.”

She had originally completed the book, under the title Bloods (meaning public-school athletic heroes), in 1969, during her chaotic early career, but lost the manuscript on a London Transport number 22 bus after a very liquid lunch. Fourteen years later, after a move to the country, the sudden threat of financial ruin forced her to write it again urgently, even dictating a chapter over the phone to the publishers.

By then Jackie Collins and Shirley Conran had published sexually explicit novels for women set among international mega-trash: Riders dwelt deep in the English countryside. Andrew Parker Bowles, the Earl of Suffolk and the Duke of Beaufort all proudly claimed to have been the inspiration for Cooper’s devastating serial rake, the Olympic showjumper Rupert Campbell-Black. The editor of Horse and Hound claimed Riders was a disgusting work, but with Rivals (1988) and Polo (1991) – the “Rutshire chronicles” trilogy – it provided most of the sex education for a generation of girls. Cooper remembered: “My Spitting Image puppet just said: ‘Sex sex sex sex sex sex.’”

Cooper was exact about her own middling place in the stratified Britain she was born into as the daughter of an army brigadier, William Sallitt, and his wife, Mary (nee Whincup), of Hornchurch, Essex. She was a rebellious boarder at the posh Godolphin school, Salisbury, pining for her pony and writing about gymkhanas, and then deliberately flunked the entrance exam for Somerville College, Oxford. She muddled through as a cub reporter on a local newspaper, the Middlesex Independent, and a dogsbody in PR.

Marriage was her first destination, to Leo Cooper, ex-army officer, sportsman and gentleman publisher, in 1961. They had known each other in childhood – she recalled seeing him at a party, throwing jelly at a spoilt brat – and met again, accidentally, after his divorce from his first wife.

Any encounter in publishing circles in the 1960s might turn into employment, and at a dinner party in 1968, Cooper, in her unique baritone, explained to Godfrey Smith, editor of the Sunday Times colour magazine, how hard was her life as a young wife: “One made love all night, then shopped all day, then died of exhaustion.” He offered her a column, which became “Jolly Super”, an experiment in a funny-sexy female voice, from 1969 until 1982; after Rupert Murdoch’s takeover of the paper, she fled to the Mail on Sunday until 1987.

Cooper’s real breakthrough was into fiction. Told that an ectopic pregnancy had left her infertile, “I sobbed all the way down Harley Street, bumping into lamp-posts”, then “got the fantastic bonus of a career … this explosion of creativity”.

She sold short stories to magazines before expanding them into novels, “permissive romances” – Emily, in 1974, then Bella, Harriet, Octavia, Imogen and Prudence, aimed at a less would-be sophisticated audience than her journalism.

Then Leo’s small military history publishing company crumbled. The couple, with two adopted children, Felix and Emily, had lived a bohemian, insolvent life – “where did the money from journalism go?” she wondered as she hid from creditors in the shed of their cottage in Putney.

They had never been candid with each other about finances and decided in their brokest year, 1982, to buy a manor house near Stroud, Gloucestershire. Leo stayed in London for half the week; Cooper joined a “dashing and exciting” Cotswold set; from that milieu – and a visit from the bank manager to warn the house must be sold if the couple could not raise hard cash – came Riders.

Like Cooper, her female characters had more responsibilities and less fun than the men; she retained her strong belief that men needed “to be honoured and praised and encouraged”; a wife’s job, as she had defined it in her 1969 manual, How to Stay Married, was to please and manage her husband, and Cooper could be smug about her perfect marital relationship.

And then a secretary in publishing, Sarah Johnson, made public the affair she had had with Leo through much of the 80s, while Jilly had been bashing away three-fingered on her portable typewriter in the country. The marriage teetered, but the couple reconciled, Cooper made public revelation of her own youthful fling, and their partnership was back in business. She went on writing to fund their life, and in later years his care and comfort: in all, about 40 books, half of them novels.

The later output, from Appassionata (1996) through to Mount! (2016), outsized preposterously in plot to keep up with the new globalised wealth, as oligarchs bought country manor houses and Gulf oil money funded racing stables, while her large casts of characters double-dealt, champagne glass in hand, in upper-crust venues. Cooper’s elan transmuted, too – in Jump! (2010), the excitement isn’t shagging in the nettles, but a heroic horse deservedly winning a close race. A late entry, Tackle! (2023), cost her seven years’ intermittent research in directors’ boxes around the premier end of English football. Some were adapted for television, most successfully Rivals (2024) as a period costume – 1980s – miniseries.

Cooper was ever-anxious (always threatening to return the advance because a book would never be good enough), yet stoic: she had crawled through a derailed carriage, clutching a manuscript, to escape from the 1999 Ladbroke Grove train crash, then tidied up before taking a taxi to the Ritz. For all her sociability she was more at ease with animals, rescue cats and mutt dogs, birds and badgers, and she fundraised for the Animals in War memorial in Hyde Park. Her appointment as OBE in 2004 was for services to literature; her CBE in 2008 and DBE in 2024 for literature and charity.

Leo, who had suffered for some years with Parkinson’s disease, died in 2013. Felix and Emily survive her.

• Jilly Cooper, novelist and journalist, born 21 February 1937; died 5 October 2025