The BBC risks propelling unsubstantiated rumours about the Royal family and their staff to credibility by broadcasting them on prime time television, it is feared, in an expose on "The Princes and the Press".
The corporation, which airs the first of a two-part documentary on Monday night, has interviewed dozens of journalists and royal commentators about the relationship between Princes William and Harry and the media.
Buckingham Palace has already threatened a boycott of future dealings with the BBC, according to reports, with the three households of the Queen, the Prince of Wales and the Duke of Cambridge uniting to complain to the corporation about a lack of transparency on what is in the documentary.
No previews were available before the programme’s broadcast, with next week’s episode expected to air allegations to which the Palace has never previously given enough credence to make a comment.
It is anticipated that the episode includes claims that members of the Royal household briefed journalists about the breakdown of relationships between the Sussexes and the rest of the Royal family and eventually leaked the bombshell news that they were leaving in order to undermine Prince Harry’s negotiations.
Buckingham Palace, Clarence House and Kensington Palace believe they have not been offered a proper right of reply to the claims. It is understood the three households have been sent a written memo by the BBC outlining the relevant part of the programme, with an invitation to contribute.
But senior aides believe they have not been given enough detail to enable them to respond properly, with the BBC refusing to disclose who was interviewed ahead of time or what proof they had provided.
A spokesman for the Sussexes did not comment on whether they had also complained or had concerns about the programme.
Amol Rajan, the presenter, said he spent 80 hours interviewing journalists involved in writing royal news from 2012 to the present, from Jonny Dymond, the BBC’s royal correspondent, to Omid Scobie, the author of the biography Finding Freedom, with whom the Duchess of Sussex allowed her communications secretary to co-operate.
Insiders fear the result will see a host of tabloid stories on which the Palace has never previously commented propelled to legitimacy.
The programme is broadcast in two parts. The first, screened on Monday night, details the media coverage of younger members of the Royal family from the Queen’s Diamond Jubilee in 2012, when the Duke and Duchess of Cambridge and Prince Harry were considered to be the bright future of the monarchy.
It tracks the positive media coverage up to Prince Harry’s engagement to Meghan Markle in 2018 and explores the Princes’ relationship with the press, including phone-hacking.
Prince Harry and Prince William timeline
The second, due for broadcast on Nov 29, is expected to go through some of the key newspaper stories uncovering fractured relationships behind closed doors, with allegations of Palace insiders briefing the media.
Much of it was filmed months ago and edited at the last minute after it needed to be updated with details of the Duchess of Sussex’s court case against the Mail on Sunday.
In a trailer for the accompanying podcast, Rajan said he wanted viewers to question how they had formed opinions on the Duke and Duchess of Sussex based on the media lens through which they were reported.
In making the programme, he said, he had interviewed "the people who wrote this very modern drama" – columnists, royal reporters and broadcasters. "Some of what they say is shocking," he said. "Some of it is plain weird. But all of it helps us understand why we are where we are."
Rajan said he was "not going to take sides in the culture wars" the younger members of the Royal family had been "conscripted into", but was seeking to "bring light where there is heat".
A source said the programme was intended to be a "cerebral" look at the Palace and press and not to be "incendiary".
A BBC spokesman said: "The programme is about how royal journalism is done and features a range of journalists from broadcast and the newspaper industry."
BBC guidelines require all news and current affairs documentaries to offer right of reply to anyone implicated in their journalism.