Channel 4 has been criticised for plans to broadcast controversial video tapes of Princess Diana opening up about her troubled marriage and public life.

The decision to air the programme ahead of the 20th anniversary of Diana's death has been slammed as the "lowest common denominator".

Titled Diana: In Her Own Words, the documentary sees the Princess of Wales speak candidly about her upbringing, early relationship with Prince Charles and relationship breakdown.

Channel 4, who will broadcast the programme on August 6, said the tapes offered an "important contribution to the historical record".

But critics on the other hand labelled the show "completely inappropriate" - with some even arguing the footage did not belong in the public domain.

The tapes - recorded by Diana's speech coach Peter Settelen - have never before been broadcast on British television - and some of the footage is being shown for the first time.

Dickie Arbiter, a former spokesman for the Queen, poured scorn on the release, saying: "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."

Meanwhile, Rosa Monckton, one of the Princess of Wales's closest friends, said the tapes should be given to Princes William and Harry and not broadcast.

She said: "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."

The tapes were returned to Mr Settelen in 2004 after a lengthy dispute with Diana's family, headed by Earl Spencer, who said the footage belonged to them.

A batch of some 20 videos had been held by Scotland Yard after being seized in a January 2001 raid on ex-royal butler Paul Burrell's home.

The content of the tapes was regarded as so sensitive that the prosecution agreed not to use them in Mr Burrell's Old Bailey trial which collapsed in 2002.

The tapes were later sold to American broadcaster NBC for an undisclosed sum and excerpts were broadcast in 2004, showing Diana talking of how Charles "leapt upon" her to kiss her at the start of her relationship.