“Vulgar, vulgar, vulgar”: that was the 1995 remark made by Lord Charteris, former Private Secretary to Elizabeth II, about Sarah Ferguson.

Thirty-one years later, it’s hard to improve on that succinct character appraisal. This morning rumours swirled that Ferguson was about to sign a seven-figure deal for an explosive memoir.

A spokesman denied it, saying: “Sarah Ferguson is not close to signing a multi-million-dollar book deal, as has been reported. She has no plans to write any tell-all memoir.”

Note the carefully worded statement. “No plans to” doesn’t mean she won’t. And this non-denial denial will have the official members of the Royal Family in a sweat – in the week Earl Spencer spilt the beans about how badly King Charles had allegedly behaved to his sister Diana, Princess of Wales.

At any moment, Ferguson could reveal or claim damaging things about the Royal Family. That’s the problem with banishing someone – as the King effectively did to both the Yorks when Andrew Mountbatten-Windsor was obliged to give up his titles last year.

Ferguson is now a dangerous loose cannon. She’s lost everything: her royal status, titles, money and the vast home, Royal Lodge, she shared with her ex-husband. For years, the Royal Family have made clear how low their opinion is of her – ever since 1992, when she was photographed having her toes sucked by Texan businessman John Bryan.

Any remaining vestiges of affection for her were blown away by Andrew Lownie’s devastating biography of the Yorks, , published last year. As the book made clear, the Yorks lived on a monstrously extravagant scale, way beyond their means, desperate for handouts and free flights from the paedophile Jeffrey Epstein.

Ferguson is presumably near-broke – although perhaps she is still subsidised by Mountbatten-Windsor. But her taste for high living will not disappear just like that.

Nor will her desperate hunger for attention. In 2005, I interviewed her in New York, where she was promoting her own Duchess of York Sandwich at Stage Deli on Seventh Avenue, promoting GourMayo, a wasabi horseradish-flavoured light mayo. It should have been called the Vulgar, Vulgar, Vulgar Sandwich.

She was rather endearing in the flesh, keen to please, with her jolly hockeysticks Malory Towers vocab. “That’s humongous,” she said of the vast sandwich. But she also knew she was there to flog her product, adding, “The portion sizes here are enormous. You’ve got to take the edge off with things like light mayonnaise.”

Her greed is second only to her stupidity. It’s one thing to flog yourself for money; quite another to do it so badly. In a 2010 News of the World sting, she offered to sell access to Mountbatten-Windsor for £500,000. Her stock has plummeted hugely even since then. But, given the jaw-dropping revelations about Mountbatten-Windsor in recent years, any juicy, fresh ones could guarantee her one last huge payday.

Whatever fragment of shame she might have possessed will be eclipsed by her need for money. While Elizabeth II was alive, Ferguson could cling to her connection to the monarch. Even after the Queen died, the Yorks were given her corgis to look after. But those dogs are their last living connection with the monarch who kept the whole institution together, despite its warring, often incompetent minor members. Now Elizabeth II is dead; there is nothing to stop Ferguson revealing her secrets in all their rip-roaring vulgarity.

It’s become clear, with memoirs by Prince Harry, Earl Spencer and now possibly Ferguson, that the non-official royals are realising it’s time to cash in, particularly in the build-up to the 30th anniversary of Diana’s death. There are rumours, too, that Harry is in talks to make a documentary about his mother in time for the anniversary.

Never has the yawning chasm between the working members of the Royal Family and the non-working ones been so stark.

In one corner, there are the King, the Queen, the Prince and Princess of Wales, Princess Anne, the Edinburghs, the Duke of Kent (91 next month), the Gloucesters and Princess Alexandra. They are still doggedly doing their duty, staying admirably discreet and avoiding commercial embarrassment.

Then there are the outcasts, topping up their current account while they still have revelations to flog. The problem with being an exile, as Harry and Ferguson have discovered to their cost, is that you are cut off from access to the golden goose: tantalising new nuggets about the Royal Family.

So, if you can’t garner fresh information, the answer is to dig deep into the past and pluck out plums that are so juicy even the passage of time can’t fade their allure.

That’s what Earl Spencer did this week in his memoir. And it looks like Harry and Ferguson will be emulating him in the coming months. Hold onto your hats – a tsunami of royal gossip is coming your way in 2027.