A former MI6 agent, Mr Richard Tomlinson (35), was yesterday questioned for two hours by Judge Herve Stephan, the French magistrate investigating the car crash in which Princess Diana was killed.
In a letter to Judge Stephan, Mr Tomlinson, who worked for MI6 for four years, claimed that the agency planned to assassinate another foreign personality in Paris.
Judicial sources said he told Judge Stephan yesterday that Mr Henri Paul, the deputy head of security at the Ritz Hotel who drove the princess and her Egyptian boyfriend, Mr Dodi Fayed, to their deaths, was an MI6 agent and that one of the princess's two bodyguards was in contact with British intelligence.
Mr Tomlinson was arrested by French police earlier this month, along with the former MI5 officer, Mr David Shayler, at the request of British authorities. Both men were allegedly preparing to divulge secrets about the intelligence agencies for which they had worked.
Mr Tomlinson was released and travelled to New Zealand in the interim. He saw Judge Stephan at his own request. Mr Shayler is still in detention while the French consider an extradition request from Britain.
Sources question Mr Tomlinson's motives for making such claims about British intelligence so near to the first anniversary of Princess Diana's death.
The intense publicity surrounding the case has inspired a great deal of fabricated testimony, and television networks have paid high prices for leaked information.
The resurfacing of a former British intelligence agent in the context of the Princess Diana investigation will doubtless prompt renewed speculation that there was a conspiracy to murder the princess and Mr Fayed.
Mr Fayed's father, the billionaire Harrod's owner, Mr Mohamed al-Fayed, has annoyed French authorities by repeatedly alluding to a plot to kill the couple.
French investigators believe the crash was caused by drink-driving at high speed. However, the theory that the royal family asked British intelligence to murder Princess Diana and Mr Fayed - rather than risk having the mother of a future king married to a Muslim - has gained wide credence in the Arab world.