Ken Wharfe said he believed the high-level surveillance is aimed at preventing Irish Republican Army assassinations, London's The Daily Mail said.
Wharfe also said Fayed family security mishandled photographers at the Paris Ritz the 1997 night Diana and her boyfriend Dodi Fayed died in an auto accident.
"The very fact that they played their cat-and-mouse game with her security to me was the beginning of the end," he said, noting that allowing the couple to pose for photos could have created a "dignified" exit, the paper said.
"If the (photographers) were managed this would never have happened. Had the security men spoken to the (photographs) at the beginning, what they would tell you is that they wanted a picture of Diana," Wharfe said during the inquest into Diana's death.
The inquest is required by British law when someone dies unexpectedly, violently or of unknown causes, but it was delayed 10 years while French and British police conducted investigations that concluded driver Henri Paul, who was also killed in the crash, was drunk and the deaths were accidental.