Mr Tomlinson, who has levelled a series of criticisms against the UK security services, is believed to have written to Judge Herve Stephan asking for an interview.

The agent, who spent six months in jail for trying to sell his memoirs in breach of the Official Secrets Act, spent two hours behind closed doors at the Palais de Justice in Paris.

Tomlinson's evidence comes almost a year to the day Diana died

He left the building without giving any details of his evidence to waiting reporters.

Conspiracy theory

Sources close to the investigation said Tomlinson claimed that Diana's driver Henri Paul, who also died in the crash along with Diana's companion Dodi Fayed, was working for UK intelligence.

He is also reported to have claimed that one of the bodyguards working for Diana and Dodi on the day of the crash - either Trevor Rees-Jones or Kes Wingfield - was a contact for UK intelligence services.

In a letter to the judge, Mr Tomlinson said MI6 was planning an assassination attempt in Paris against another foreign personality.

Arrested

Mr Tomlinson was arrested in Paris earlier in August at the request of the UK Government after being freed from jail, but he was later released after it was decided he was not a threat to security.

He was arrested alongside ex-MI5 agent David Shayler, who is facing charges under the Official Secrets Act.

Driver Henri Paul also died in the crash

Mr Tomlinson travelled from Paris to his native New Zealand where he had been thought to be living.

In New Zealand, he was prevented from boarding a plane to Australia because of fears he was intending to reveal secrets.

An Auckland court placed a gagging order on Mr Tomlinson to stop him disclosing further details about MI6 activities.

Outspoken critic

The former MI6 agent has been an outspoken critic of his former employers, accusing the security services of being inefficient and unaccountable.

French investigators have sought to quash speculation that MI6 was involved in the Paris crash.

They say they have found no evidence to support claims that Diana and Dodi Fayed were the victims of an assassination conspiracy.

Judge Herve Stephan's headquarters are sticking to their policy of "no comment" on the evidence Mr Tomlinson gave.

Mr Tomlinson's lawyer Madame Levey also declined to comment about what her client discussed with the judge.