Channel 4 has said it will go ahead with plans to broadcast images of the crash that killed Princess Diana despite a plea from her sons not to do so, although it will air an extra programme to debate the issues raised.

The new head of Channel 4, Julian Bellamy, said the broadcaster had weighed up the concerns of Princes William and Harry but believed there was a "legitimate public interest" in the documentary, Diana: The Witnesses in the Tunnel, and that it would air as planned tomorrow night at 9pm.

"We would like to make clear that it was not our intention in commissioning this programme to cause them distress and we do not believe the film is in any way disrespectful to the memory of Princess Diana," he said.

However, in a concession to the growing storm surrounding the documentary, Mr Bellamy said an extra programme would air at 11pm in which "the issues raised by the channel's decision to show the programme will be debated".

A Channel 4 source said the debate show was part of the broadcaster's new policy of addressing concerns about its programmes on air, following the Celebrity Big Brother racism storm.

"This is recognition that if we are doing things which are going to be a matter of public debate and prompt viewer responses it is important to have an outlet to debate these issues," the source said. "It is a learning point from Big Brother."

A Channel 4 source said a screening of the Princess Diana documentary was held for the Prince of Wales' press secretary, Paddy Harveston, and William and Harry's private secretary, Jamie Lowther-Pinkerton, although the two princes had not seen it themselves.

Mr Bellamy added that no images of the victims of the crash would be shown as Channel 4 had made a "clear decision from the outset to uphold the consensus quite properly reached by the British media" not to use the pictures.

"Those images that are included have been selected with due consideration for the feelings of the relatives of those involved," he said.

"We believe, in this context, the photographs and the assembled interviewees provide the most detailed and credible eyewitness account yet delivered of an event of international importance that for 10 years has been obscured by claim and counter-claim," Mr Bellamy added.

"They support the first-hand testimony of passers-by and the photographers at the scene who have been publicly criticised and condemned for their behaviour that night.

"The programme goes no further visually or in tone than many previous British TV and newspaper reports.

"A number of the pictures in the documentary have already appeared in the British media in a similar context."

Channel 4 pointed out that the BBC's Panorama had used three colour pictures from inside the tunnel in a documentary the week after the accident and these images were also used in another BBC documentary, Diana: The Conspiracy Files, in December last year.

However, the BBC later asked Channel 4 to clarify that Panorama had "never broadcast images showing Princess Diana or other occupants of the car at the crash scene as a matter of policy".

A BBC spokesman added that only long-range pictures of the tunnel had previously been used.

Channel 4 also said they had been published in the Sunday Times and one was used in a recent Channel Five documentary, while the image of a French medic giving Diana oxygen was used in the same form on the front of The Sun in July last year.

The broadcaster has also released a letter which it sent to Clarence House in reply to the request from the two princes to remove the offending images.

The comprehensive three-page letter from Channel 4 director of television and content, Kevin Lygo, expressed regret at the princes' distress, but again refused to back down.

"This is in our view a legitimate media analysis of events which, whilst inevitably personally distressing, concerns matters of immense public interest which have been (and are likely to continue to be) the subject of ongoing and extensive worldwide reports and comment over a significant period," he said.

· This article was amended on Wednesday June 6 2007 after Channel 4 made changes to its original statement. The following information has been added: However, the BBC later asked Channel 4 to clarify that Panorama had "never broadcast images showing Princess Diana or other occupants of the car at the crash scene as a matter of policy". A BBC spokesman added that only long-range pictures of the tunnel had previously been used.

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