Briefing: Diana's 'rock' to be quizzed about missing letters

Royal butler Paul Burrell and the princess's sister take to the stand this week. Expect more revelations about spies and views of relationships – with lovers and the palace

Why is this week so important?

Tomorrow, potentially the most important witness to have appeared so far at the inquest into the death of the Princess of Wales will walk into court. Paul Burrell, Diana's former butler whom she described as her "rock", is expected to tell the jury that it was common practice for communications with the Royal Family to be monitored by the security services. He may also shed light on letters once in the princess's possession, and on her fears that she might be the victim of an accident. Diana's sister, Lady Sarah McCorquodale, will also appear and will be asked about the whereabouts of the missing letters from the Duke of Edinburgh, in which he allegedly threatened her.

The story so far

The inquest opened on 2 October, presided over by Lord Justice Scott Baker, who promised a "vigorous and searching inquiry" into the deaths of Princess Diana and Dodi Fayed in a car crash in Paris on 31 August 1997. The intention is to provide a definitive answer to the slew of conspiracy theories and claims that subsequently have emerged, led by those championed by Mohamed al-Fayed. Shortly before the hearing began, Mr Fayed told reporters he hoped the inquest would conclude that his son and Diana were murdered by the Royal Family. Lord Justice Baker told the 11 jurors they must decide four things: who died, where, when and how.

Highs and lows of the inquest?

The jury was shown pictures of Diana taken by paparazzi in the Pont d'Alma tunnel shortly after the crash. Diana's stepmother, Raine, Countess Spencer, told how the princess was "deeply and blissfully" in love with Dodi and that they were likely to have married, although she dismissed the idea that Diana was pregnant. Letters between the princess and the Duke of Edinburgh revealed an unexpectedly gentle side to his nature; in them he said he would do his best to help Diana and Prince Charles repair their failing relationship, while admitting he had "no talents" as a marriage counsellor.

Conspiracy or accident?

François Levistre, driving in front of Diana's car, described how it was overtaken by a motorbike inside the underpass, while other witnesses said her Mercedes may have suffered a bump with a large, dark, car. Other witnesses recounted the involvement in the accident of a white Fiat Uno. This car has never been traced. But an accident investigation expert said the crash was probably caused by the driver's "over-reaction" in avoiding the mystery Fiat and that Mr Paul's consumption of alcohol would also have contributed. Sebastian Trotte, a former barman at the Ritz, said Mr Paul did not appear drunk before he left the hotel but a second Ritz barman, Alain Willaumez, said Mr Paul was not only drunk but "walking like a clown" before the accident.

What revelations came out last week?

On Monday the inquest heard from Grahame Harding, a security expert, who said a suspected bugging device may have been found in Diana's Kensington Palace apartments. The princess had her apartment swept for bugs four times before a signal was discovered, although Mr Harding admitted it could have come from a radio or a mobile phone. The jury also heard from Rodney Turner, a personal friend of the princess, who said Diana had told him her relationship with Dodi had ended a few weeks before the couple died.

On Wednesday Ken Wharfe, a former personal protection officer for the princess, claimed that the famous "Squidgygate" tape of a mobile phone call between Diana and her then lover James Gilbey, in which he called Diana "Squidgy", was picked up by GCHQ, the Government's listening centre, and repeatedly broadcast over the airwaves for radio buffs to pick up.

Simone Simmons, a complementary therapist and friend of Diana's, told the inquest that the Duke of Edinburgh had written two "nasty" notes to Diana in 1994 and 1995, although she did not reveal their contents.