Security services were monitoring Diana, Princess of Wales, and Dodi Al Fayed in the month before their death, a Scottish court has heard.
Mr Al Fayed believes his son and Diana were murdered
The Court of Session in Edinburgh was also told that their driver Henri Paul may have been an MI6 informant.
Harrods owner Mohamed Al Fayed is challenging a refusal to hold an inquiry in Scotland into their deaths.
The tycoon, who was at the Court of Session hearing in Edinburgh, believes the pair were murdered.
He also insists that the full facts of the crash in Paris on 31 August, 1997, have never been revealed.
His lawyer Richard Keen QC told the court that they had numerous arguments to cast doubt on the French police' s verdict that Dodi and Diana's deaths were an accident.
None of the 10 traffic cameras on the route from the Ritz Hotel to Dodi's flat in Paris was working at the time of the crash, he said, and yet a motorist was fined for speeding 15 minutes earlier based on video evidence on a speed camera near where the couple's Mercedes crashed.
In his submission, Mr Keen said Diana and Princes William and Harry were being monitored from around 10 July, 1997, when they arrived at the Al Fayed estate in St Tropez in the south of France.
By August press speculation was intensifying that the couple were about to
announce their engagement, fuelled by comments Diana made about an impending statement that would cause "shock and surprise".
After the couple arrived at Beauvais Airport on 30 August, Mr Keen told the
court: "As a matter of practice French security reported the arrival of the
princess to the UK embassy assuming they were not aware of it.
"The UK embassy announced that she was not the subject of any monitoring in Paris.
"It said it was not aware of her presence in Paris on 30/31 August. Consequently they said they could not assist in any matters relating to the crash or the circumstances leading up to the crash as they were not involved in any monitoring or security of the Princess of Wales.
"The petitioner (Mr Al Fayed) has real grounds to call into question the credibility and reliability of that statement."
Mr Keen also told the court the US National Security Agency had confirmed the princess was the subject of monitoring at the time of the crash.
But he said more than 1,000 pages of documents relating to the crash could not be made public in America for "national security" reasons.
Mr Keen said the surveillance may have been carried out by the US on behalf of the UK security services.
The crash site became a shrine to Diana
He also told the court of the explosive claims made by former MI6 agent
Mr Keen said Mr Tomlinson had confirmed Diana was being monitored by the UK security service in France and that MI6 paid a "long standing informant" at
the Ritz Hotel in Paris.
He told the court Paul earned about £20,000 as assistant head of security at
"Subsequent to the crash he maintained 13 different bank accounts in Paris
that contained in excess of 1.2 million French francs, which might suggest that he had some form of part-time job," Mr Keen said.
Mr Tomlinson also claimed reports of a "blinding flash" in the tunnel prior to
the crash and the reported involvement of another vehicle mirrored plans he had seen in 1992 for the attempted assassination of former Yugoslav President Slobodan Milosevic.
When he arrived at the court on Monday, Mr Al Fayed said: "What I am doing I am doing for the nation and for the ordinary people."
He said as a resident of Scotland he was looking to the Scottish courts to secure his rights.
When his request for an inquiry was rejected earlier this year, Mr Al Fayed was told it was because the crash was outside Scottish jurisdiction because it happened in Paris.
There have been no inquests in the UK into the death of Dodi and Diana after six years, and Mr Al Fayed has always maintained there has been a conspiracy or cover-up to conceal security services involvement in his son's death.
He has not enjoyed legal success in England or France in his efforts to secure a public inquiry.