Dame Barbara Cartland was dead on arrival. The doctor tasked with delivering her approached Barbara’s father, Bertie, and announced the birth was not going well and they could either save the life of his wife or his new daughter.

“Damn the bloody child,” Bertie is reported to have bellowed. “Save my wife.”

Sure enough, the doctor declared the child dead, only to quickly upgrade her condition to “alive” when she started screaming. It was a typically dramatic beginning to a life mired in drama.

Barbara Cartland released over 700 books in her lifetime, at one point pumping out 23 in a single year, sold books in the millions (possibly billions), was named the top-selling author in the world by the Guinness Book of Records and became one of the most recognisable figures in British culture during the 70s and 80s.

Always dressed in pink with a candy-floss mound of white hair, boot-polish mascara and a Pekingese dog tucked under her arm, she was both ridiculed and ubiquitous, churning out quite tame romantic literature, with many heaving bosoms but no actual intercourse, featuring virginal heroines and aristocratic men. It was safe, escapist and not too smutty. Even if you couldn’t name a single one of her books, everyone knew exactly who she was.

“She’s quite hard to resist,” author and broadcaster Matthew Sweet tells me. “She’s a big figure, but she’s also unregarded. And she’s also slipping from the cultural memory. If you’re 30 or under, it’s very unlikely that you’ll know her.”

Sweet has written a hugely entertaining biography of Barbara Cartland, entitled , which lifts the lid on her extraordinary life and vast output. Sweet tries to get under the skin of Cartland and attempts to ascertain what drove her to write and release quite so much.

“The desire to do it at all, I think, is all a consequence of her grandfather’s suicide,” Sweet explains to me. “It’s that bullet that explains the momentum of everything.”

Cartland was born in 1901 into a life of wealth and privilege. But all of that was about to change dramatically. When she was two, her grandfather James Cartland shot himself. He left a business in ruins and, in Bertie, a gadabout son who had never worked and was ill-equipped for the realities of life. With Bertie at the helm, the young family struggled – with money, with standing and with the ignominy of a suicide in the family.

From then on, they were constantly in survival mode. This never left Cartland, who was always striving for security. As a thrusting young woman in the 1920s, she worked hard to be seen in the society pages, was courted by a bevy of unsuitable young men with names like Pingo and Nigs, began to write an anonymous gossip column surveying the scene around her and eventually turned to fiction. 1925’s was her first romantic novel. Setting a trend for most of her career, reviews were mixed, but Cartland was on her way. Hundreds of books, two marriages, three children and a tumultuous life followed.

Sweet was allowed unparalleled access to the Cartland archive. Since her death in 2000, her glamorous country pile, Camfield Place, has not been touched.

“This will never happen again,” Sweet explains. “I will never walk through the door of the house of a subject that has been left untouched for a quarter of a century and be told, ‘Just go and rummage where you want.’”

As Sweet discovered, the Cartlands were far from conventional. Cartland and her brother Ronnie would gleefully send letters filled with their sexual exploits and all the latest gossip to their mother Polly. As Ronnie was both gay and a Conservative MP, this practice could have had grave implications. Cartland expected and encouraged the same behaviour from her own daughter Raine.

“There is decorum to be observed,” Sweet reveals. “Particularly when you’ve got access to very intimate private papers. And there were one or two things that I didn’t put in because I thought they were just too much.”

This slightly boggles the mind, as is crammed full of jaw-dropping incidents and details. Wild affairs, even wilder parties, bitter divorces, experimental aviation, campaigns for Romany rights, tragic deaths, accusations of plagiarism, psychics, quack medicines, political scandal and hundreds and hundreds of books drive the story along at breakneck speed. On the turn of every page, Cartland does something else completely extraordinary. The acres of unexplored documentation at Camfield constantly revealed unexpected gems.

“There’s lots of correspondence with the King in Camfield,” Sweet tells me. “Barbara had good relationships with a lot of people in the royal family. And there’s a warm, friendly correspondence between her and Diana.”

In a curious turn of events, the Cartlands and Diana’s family the Spencers grew closer when Barbara’s daughter Raine married John Spencer, Diana’s father. It’s safe to say the Spencer children were not huge fans of their new stepmother.

“Raine was very take no prisoners and very commanding,” Sweet explains. “And I think they thought that their father had been captured in some way.”

Raine attempted to win over her youngest stepdaughter Diana by providing her with her mother’s novels. There’s a photograph of the 13-year-old Diana, curled up on the sofa reading The Flame is Love. Raine also started selling Cartland’s books in the gift shop of the Spencer’s stately pile, Althorp.

As Diana was a fan, and Charles a correspondent, Cartland felt enmeshed in their relationship, occasionally hinting that she was responsible for the whole thing. Despite this, an invite to the wedding of the century never hit her doormat.

“The reason why she isn’t at the wedding is that she tried to make money out of it,” Sweet tells me, referring to Cartland’s scheme involving daytrippers having tea at her home, then lunch with “a real earl and countess” (Raine and John), at Althorp, all for a fee. As this took place during royal wedding fever, a number of undercover reporters signed up. “Barbara can never help herself,” says Sweet. “Anything that could be turned into expanding the empire or furthering the brand, she couldn’t resist.”

Her plans to reconcile the couple as the marriage failed, in the form of Charles making a televised public address to the nation while wearing “a uniform of some sort”, was not taken up. And when John died, Raine was rigorously evacuated from Althorp and the gift shop shorn of dog-eared Cartlands.

Despite the royal snubbing, Cartland continued releasing books to avid fans up until her death in 2000. In her lifetime, she was a phenomenon. But without the Dame herself to keep the Cartland brand in the public eye, she’s drifted out of public consciousness.

But Sweet hopes to keep Cartland on the cultural map. Her books may no longer sell in the millions, but her exceptional life, which touched on so many aspects of 20th-century history, demands to be celebrated.

“She was a maximalist,” Sweet explains. “Ultimately, what she really wanted was people not to look away.”

‘The Great Dictator’ by Matthew Sweet is published by Hodder & Stoughton on Friday