A leading barrister has called for a new investigation into the death of Princess Diana, which he insists was not an accident. Michael Mansfield QC made the remarks ahead of the 20th anniversary of the Princess of Wales's death in Paris.

Mansfield is adamant that police did not properly investigate a note written by Lady Di before her death in which she claimed that her ex-husband Prince Charles was planning her death in a road accident.

Mansfield, who represented the Bloody Sunday families and the Guilford Four, made his comments to a US documentary exploring alternative theories about Diana's death, The Sun reported.

He said: "If you find a body at the bottom of the cliffs in Dover and the person has left a note saying, 'I'm going to end up at the bottom of the cliffs, dead' and, in the note, she'd indicated who she thought would be responsible for her death, I think the first port of call is to say, 'Hmm, well there may be something in this'."

On 31 August 1997 Diana and her lover Dodi al Fayed were killed when the Mercedes they were travelling in crashed into a pillar in The Place de l'Almaunderpass, Paris, while travelling at around 105 km/h (65 mph).

The tragedy prompted an unprecedented outpouring of grief in the UK while the Royal Family were criticised for their initial response

Mansfield represented Dodi's father Mohammed Al Fayed during the original inquest. Fayed has long maintained that his son and Diana were killed as a result of an establishment plot although this view has not been supported by various independent inquests into the deaths.

The US TV show, which is aired on 26 August, considers a range of conspiracy theories that have circulated in the 20 years since that fateful night in Paris.

One of them claims that Diana was killed because she was carrying Muslim Dodi's child.

Diana crash
Aphoto taken 31 August 1997 shows the wreck of the Mercedes in which British Princess Diana, her friend, Dodi al-Fayed, and their chauffeur, Henri Paul, died in a high-speed crash while fleeing press photographers in the Alma bridge tunnel. Getty

The 20th anniversary has prompted a regurgitation of a number of these theories and also of the national grief experienced when Diana – the People's Princess – died.

Princes William and Harry and Princess Kate will tour the garden at Diana's former home on the eve of the 20th anniversary of her death as the family try to cope with immense personal pain away from the inevitable media circus.

Diana was once the most photographed woman in the world. IBTimes UK marks the 20th anniversary of her death by looking back at her life through 100 photos.

Hillsborough inquest
Michael Mansfield QC arrives at Birchwood Park to hear the conclusions of the Hillsborough inquest in Warrington Christopher Furlong/ Getty Images