Examining the “circumstances around the decision of the Sussexes to step down from their senior royal roles”, it details the various legal cases served by Prince Harry and Meghan, and discusses how the relationship between Diana, Princess of Wales, and the press affected her two sons.

The Sunday Telegraph understands it will include coverage of the Martin Bashir scandal, in which the disgraced BBC journalist was found to have used falsified documents to convince the late Princess to give an interview to Panorama.

The programme was being edited until the last minute this week to take in developments in the Duchess of Sussex vs Mail on Sunday case, in which the former working royal apologised for failing to remember she had authorised her then-press secretary to brief her biographers.

It could include an overlooked detail in the evidence, in which the Mail on Sunday’s editor Ted Verity said that in 2020 he “had a meeting with a senior member of the Royal Household” with “direct knowledge” of how a letter from the Duchess to her father was drafted.

‘High-grade information’

“This was not gossip or tittle-tattle: it was what I considered to be high-grade information from a serious individual in a position of authority and responsibility who knew the implications of what they were telling me,” he said in a witness statement.

Lawyers for the newspaper group later confirmed to the court that the source was not Jason Knauf, the Sussexes’ former press secretary who eventually provided on-record evidence revealing the couple had authorised him to brief the authors of their biography.

The BBC has not confirmed which elements considered for the documentary will make the final cut.

No previews of the show were made available to the palace, which was asked to respond to a series of allegations in it but believes it did not have enough information to do so.

One palace source said the approach amounted to little more than a “fishing expedition” aimed at getting aides to give credence to stories they had never commented on before, calling the content “unfounded conjecture”.

“These are speculative rumours,” said another, of tabloid stories covered in the programme.

The BBC is fully standing by the programme, made by Amol Rajan, with sign-off for the final episode to be broadcast going to executive level.