Channel 4 has defended the use of controversial video tapes of the late Diana, Princess of Wales, in a forthcoming documentary, describing the material as an "important historical source".
Featuring the footage in the documentary Diana: In Her Own Words has been strongly criticised by royal commentators and Rosa Monckton, one of Diana's closest friends, who said it was a "betrayal of her privacy".
But the broadcaster said the programme, due to be screened on Sunday, gave the Princess a voice and placed it "front and centre" in the run-up to the 20th anniversary of her death in a car crash in Paris on August 31 1997.
The documentary features Diana speaking candidly and informally about her upbringing, her courtship with the Prince of Wales, her troubled marriage and her public life.
Kensington Palace, the royal household of Diana's sons, the Duke of Cambridge and Prince Harry, has declined to comment about the documentary.
Channel 4 said in a statement: "The excerpts from the tapes recorded with Peter Settelen have never been shown before on British television and are an important historical source.
"We carefully considered all the material used in the documentary and, though the recordings were made in private, the subjects covered are a matter of public record and provide a unique insight into the preparations Diana undertook to gain a public voice and tell her own personal story, which culminated in her later interview for Panorama.
"This unique portrait of Diana gives her a voice and places it front and centre at a time when the nation will be reflecting on her life and death."
The tapes - recorded by Diana's speech coach Peter Settelen - have been screened in the US but never broadcast on British television, with some of the footage due to be shown for the first time.
Ms Monckton has said the tapes should be given to the princes and not broadcast.
She told the Guardian: "This doesn't belong in the public domain.
"It is a betrayal of her privacy and of the family's privacy. I certainly don't think they should be broadcast."
Diana hired Mr Settelen between 1992 and 1993 to help with her public speaking voice, following her collaboration with author Andrew Morton on a biography, and ahead of her bombshell Panorama interview in 1995.
The footage, captured at her private residence in Kensington Palace, shows Diana rehearsing her speaking voice and reflecting at length about her life.
Dickie Arbiter, a former spokesman for the Queen, told Sky News: "It is absolutely shameful that these tapes have been made available.
"It seems that there is sort of grubby blood money running around.
"Channel 4 should really think deeply, not about ... their ratings figures but about the people and family who are still around who will find this very hurtful."