Government departments are doing "anything to avoid" sharing information about Prince Andrew's past business dealings.
The claim comes from author Andrew Lownie who's been working for four years on a new book about the Duke of York.
He has submitted over a hundred requests to Whitehall departments only to find that information "has vanished".
Speaking to Sky News, he said: "I used to write about the intelligence services, and I found that was a lot easier, a lot more open and transparent than the Royal Family.
"I have tried, through the Freedom Information Act, to get access to any of the paperwork for Andrew, a special representative between 2001 and 2011 when he was taxpayer-funded, a public servant", but explaining how his requests have been rejected he said "this stuff has vanished".
'It's like playing whack-a-mole'
"The Foreign Office claimed not to know anything about it. The Department of Business and Trade know nothing.
"It's like playing whack-a-mole. It's real Yes Minister stuff, anything to avoid releasing this information."
Interest in Prince Andrew's finances has increased in recent months after it was revealed that the King was no longer paying him an allowance, raising questions about how he is able to pay for his home on the Windsor Estate, Royal Lodge, and security.
The prince's time as trade envoy for the UK may be significant because it was potentially a lucrative time for him, giving him access to business contacts around the world.
Information withheld 'in accordance with the acts'
A Department for Business and Trade spokesperson said: "The department has complied with its obligations under the Freedom of Information Act and Public Records Act and maintains that information has been withheld in accordance with the acts.
"This includes an ICO (Information Commissioner's Office) decision notice which outlined that the commissioner did not need to take any further steps."
When asked, the Foreign Office told Sky News: "The FCDO (Foreign, Commonwealth and Development Office) takes its obligations under the Freedom of Information Act very seriously."
It comes as a Chinese businessman - described as a "close confidant" of Prince Andrew - was barred from entering the UK over national security risks.
Known as H6, the man was invited to the duke's birthday party in 2020, and was told by Andrew's aide Dominic Hampshire that he could help in potential dealings with Chinese investors. A judge ruled the Chinese businessman had an "unusual" degree of trust from the royal.
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On Friday, the duke said he "ceased all contact" with the businessman after concerns were raised by the government.
Andrew met the individual through "official channels" with "nothing of a sensitive nature ever discussed", a statement from his office said.
Growing call for accountability
Former chair of the public accounts committee between 2010 and 2015, Baroness Margaret Hodge, has joined calls for less secrecy generally around the royal finances.
She told me: "I find it really difficult to believe that the departments for whom Prince Andrew had contact when he was an envoy have not got the records.
"They will have those records, they obviously just don't want to share them. And that really says it all.
"I want a Royal Family that is well-funded: they're a precious and valued institution in our society but going with that funding must come some accountability."
The palace believes that as a non-working royal, the duke's income and tax arrangements are a matter for him and HM Revenue and Customs.
In terms of how he is paying for Royal Lodge, Sky News understands the royal household has been given assurances that his sources of income are all above board, however, it is not in their remit to vet or approve those sources.
It sees it as a job for the Crown Estate which manages properties in the likes of the Windsor Estate.
But Royal Lodge is of interest more generally to the family.
As the former home of the Queen Mother, it's been suggested that potentially other members of the family may be interested in living there in the future, from the Prince and Princess of Wales to Queen Camilla looking at it for her family.
'Opaque' and 'confusing'
However Robert Hardman, journalist and author of Charles III: New King. New Court, says: "Everything to do with Prince Andrew is opaque, is confusing, people don't really want to talk about it because his situation is a distraction."
He added: "I think the real question is not what's happening today, it's what's happening in a few years down the line, what happens if his savings run out, these sources of income such as they are at the moment, what if they run out and suddenly he can't afford to pay for the maintenance or the protection, what happens to the lease then?
"Does the Crown Estate then say, 'Well, actually the terms of the lease have been forfeited?' We just don't know.
"It is a private financial matter for him but given the prominence of the house and its history and its connections, then the media are clearly going to carry on taking a keen interest in it, as are the Crown Estate and as are ultimately the Treasury."
Prince Andrew's television interview five years ago about his links to convicted paedophile Jeffrey Epstein was meant to shut the scandal down and allow him to get back to public duties without that distraction.
Instead, it had the opposite effect.
This year, he has only been seen once officially in front of the cameras, as he appeared to lead the family as they walked to the chapel at Windsor for a memorial service in February.
This Christmas we may again see Andrew with the rest of the family going to church at Sandringham, always a sign that he hasn't been entirely left out in the cold by his relatives.
But he still lives with the repercussions of the Jeffrey Epstein saga, his extraordinary downfall meaning questions will continue to remain about him, how he lives and his finances.
(c) Sky News 2024: Prince Andrew: Paperwork relating to Duke of York's past business dealings 'has vanished',