The Duke of Cambridge has issued a scathing statement criticising the BBC for its failings around his mother’s Panorama interview, which he says exacerbated her “fear, paranoia and isolation”.

William said he was left with “indescribable sadness” to know the corporation’s shortcomings had “contributed significantly” to Diana Princess of Wales’ state of mind in the final years of her life.

“She was failed not just by a rogue reporter, but by leaders at the BBC who looked the other way rather than asking the tough questions,” the duke said.

The Duke of Sussex in a separate statement said about his mother: “The ripple effect of a culture of exploitation and unethical practices ultimately took her life.”

An inquiry found the BBC covered up “deceitful behaviour” used by journalist Martin Bashir to secure his headline-making world exclusive interview with Diana, and “fell short of high standards of integrity and transparency”.

The journalist was in “serious breach” of the BBC’s producer guidelines when he faked bank statements and showed them to Earl Spencer to gain access to the princess in 1995, a report by Lord Dyson said.

The future king said his mother’s appearance on Panorama contributed to “making my parents’ relationship worse”.

William called for the documentary never to be aired again and said the BBC’s failings had not only let his mother and family down but the public as well.

The BBC has written to the royal family to apologise for the circumstances surrounding the interview – in which Diana said: “Well, there were three of us in this marriage, so it was a bit crowded”, a reference to Camilla Parker Bowles – who Charles later married.

Personal expressions of regret have been sent to the Queen, Prince of Wales, the dukes of Cambridge and Sussex, and Diana’s brother Earl Spencer.

The earl has said he “draws a line” between the Panorama interview with his sister Diana, Princess of Wales and her death two years later.

William said in his statement: “The interview was a major contribution to making my parents’ relationship worse and has since hurt countless others.

“It brings indescribable sadness to know that the BBC’s failures contributed significantly to her fear, paranoia and isolation that I remember from those final years with her.

“But what saddens me most, is that if the BBC had properly investigated the complaints and concerns first raised in 1995, my mother would have known that she had been deceived.”

He ended with the words: “In an era of fake news, public service broadcasting and a free press have never been more important. These failings, identified by investigative journalists, not only let my mother down, and my family down; they let the public down too.”

Harry praised Diana in his statement, saying: “Our mother was an incredible woman who dedicated her life to service. She was resilient, brave, and unquestionably honest.

“The ripple effect of a culture of exploitation and unethical practices ultimately took her life.

“To those who have taken some form of accountability, thank you for owning it. That is the first step towards justice and truth. Yet what deeply concerns me is that practices like these — and even worse — are still widespread today.

“Then, and now, it’s bigger than one outlet, one network, or one publication.

“Our mother lost her life because of this, and nothing has changed. By protecting her legacy, we protect everyone, and uphold the dignity with which she lived her life. Let’s remember who she was and what she stood for.”

Charles, Earl Spencer, has told a new Panorama programme that the consequences of the princess’ decision to do the interview contributed to her death in a car crash in Paris on August 31 1997.

Diana and her lover Dodi Fayed died when their car crashed in the Pont de l’Alma tunnel as they were being pursued by the paparazzi.

At the time of her death the princess had been divorced for a year after the final stages of her marriage break-up had become public.

Diana’s brother told Panorama: “The irony is that I met Martin Bashir on the 31st of August 1995, because exactly two years later she died, and I do draw a line between the two events.

“It’s quite clear from the introduction that I sat in on the 19th of September 1995 everyone was going to be made untrustworthy, and I think that Diana did lose trust in really key people.”

Lord Dyson, former master of the rolls and head of civil justice, was appointed to look into the circumstances surrounding the Bashir interview.

The journalist had commissioned documents purporting to show payments into the bank account of Alan Waller, a former employee of Earl Spencer, Patrick Jephson, Diana’s private secretary, and Richard Aylard, private secretary to the Prince of Wales, Lord Dyson’s report noted.

The documents falsely suggested the individuals were being paid for keeping the princess under surveillance.

Lord Dyson’s report said: “By showing Earl Spencer the fake Waller and Jephson/Aylard statements and informing him of their contents, Mr Bashir deceived and induced him to arrange a meeting with Princess Diana. By gaining access to Princess Diana in this way, Mr Bashir was able to persuade her to agree to give the interview.”

An internal 1996 BBC investigation into the matter led by former director-general Lord Tony Hall, who was director of BBC news and current affairs at the time, and another senior manager Anne Sloman, was described as “woefully ineffective” by Lord Dyson’s report.

The document found the BBC inquiry “did not scrutinise Mr Bashir’s account with the necessary degree of scepticism and caution”, despite the fact he “had lied three times when he said that he had not shown the fake statements to Earl Spencer”.

It also said Bashir was “unable or unwilling” to offer a credible explanation as to why he had commissioned the fake statements and why he had shown them to the earl. Diana’s brother was not approached in 1996 to give his version of events.

The report said: “They accepted the account that Mr Bashir gave them as truthful.”

Lord Dyson added: “I have concluded that, without justification, the BBC covered up in its press logs such facts as it had been able to establish about how Mr Bashir secured the interview, and failed to mention the issue at all on any news programme, and thereby fell short of the high standards of integrity and transparency which are its hallmark.”

Lord Hall has apologised, saying: “I have read Lord Dyson’s report and I accept that our investigation 25 years ago into how Panorama secured the interview with Princess Diana fell well short of what was required.

“In hindsight, there were further steps we could and should have taken following complaints about Martin Bashir’s conduct.

“I was wrong to give Martin Bashir the benefit of the doubt, basing that judgment as I did on what appeared to be deep remorse on his part.”

A handwritten note from Diana on Kensington Palace notepaper, which was part of the evidence in the inquiry, said Bashir did not show her any documents or give her any information “that I was not previously aware of”.

She said she took part in the interview “without any undue pressure” and had “no regrets concerning the matter”.

Bashir has apologised for faking the documents and said it was “a stupid thing do to do”, and “an action I deeply regret”, but maintained it had “no bearing whatsoever on the personal choice by Princess Diana to take part in the interview”.

He added: “Evidence handed to the inquiry in her own handwriting (and published alongside the report today) unequivocally confirms this, and other compelling evidence presented to Lord Dyson reinforces it.

“In fact, despite his other findings, Lord Dyson himself in any event accepts that the princess would probably have agreed to be interviewed without what he describes as my ‘intervention’.”

He said he will “always remain immensely proud of that interview”.