Author David McClure has pored over the royal finances to calculate the Queen’s true worth for Royal Legacy, the first full-length book on the regal balance sheet for 20 years.
He puts the figure at around £300million, less than the £330million attributed to Her Majesty by last year’s Rich List.
Ex-Reuters journalist McClure said: “To be fair, there is an element of guesswork in all lists of the mega-rich since without access to their bank accounts or tax returns valuers can do no more than speculate about the exact size of many hidden assets.
"But I think it is fair to say that the Queen is not as wealthy as is often made out and could be viewed as asset rich and cash poor.”
The Queen’s landed property is easiest to put a price tag on.
Balmoral and Sandringham, the only royal residences the 88-year-old monarch owns privately, have been valued at more than £60million.
However, some of her most valuable possessions are kept under wraps, or rather protective sheets.
She inherited the Royal Philatelic Collection, the world’s most comprehensive collection of postage stamps of Britain and the Commonwealth
Many of the most prized pieces were assembled by her father, George V.
With just one set of penny blacks valued at £4million, the Queen’s total collection must be worth £10million although some estimates put the figure at £100million.
The Queen also owns a valuable art collection worth many millions.
The Crown Jewels and the Royal Collection are inalienable state treasures and do not figure in her private wealth.
She inherited the Queen Mother’s collection of paintings and jewellery with an estimated value of £60million.
The Queen is also thought to own shares in blue chip British companies rumoured to be worth as much as £105million.
The income the Queen derives from the 18,458 acres of the Duchy of Lancaster has also been on the rise.
The jewel in the crown is the Savoy Estate, two acres of prime real estate in London between the Savoy Hotel and Somerset House.
Commercial rents have risen from £3.75million in 1992 to £13.6million in 2014.
For all her renowned thriftiness, the Queen harbours one indulgence... horses.
In 2001, her 30 racehorses and 26 broodmares were valued at £3.6million although by 2011 she reduced her stable to about 25 horses.
However, with overheads as high as Becher’s Brook, it is a moot point whether her equine venture has ever made a profit.