The footage, showing the Princess in her underwear, is thought to have been shot through a window at Highgrove, the Prince of Wales's country home, near Tetbury, Gloucestershire. It appears to confirm the Princess's fears that she was spied on. The video is thought to be at least five years old.
The 80-second tape appears to show the Princess stripping down to her sports pants and bra, kissing Mr Hewitt, riding on his back and fighting with pillows. The video, believed to have been stored in a vault in the United States, was offered to the Sun during a meeting last Friday in west London.
The paper said an American lawyer claimed to be acting for a group of soldiers or bodyguards led by a man known only as "The Sergeant". He said the video would have been used against the Princess if she had "cut up rough" during the recent divorce negotiations with the Prince.
A Buckingham Palace spokesman refuted suggestions that the film could have been used for blackmail: "The Princess admitted an affair with James Hewitt when she appeared on BBC TV's Panorama - before the divorce negotiations. So how could this video have been used against her?"
The Princess has claimed her phone calls were tapped, listening devices installed in her private apartments and her mail intercepted.
Mr Hewitt told the Sun that he and the Princess were "undoubtedly" spied on when they were together. "One theory was that the Princess's divorce settlement was only half of what she wanted because of this sort of material," he said.Reuse content