The Big Question: Can the Diana inquest tell us anything we did not already know?

What will it cost and how long will it take?

The jury of six women and five men who were sworn in yesterday are expected to hear up to six months of testimony to determine what happened on 31 August 1997 when Diana, Princess of Wales and her companion, Dodi al Fayed, died in a car crash in a Paris underpass. As many as 70 witnesses may be called to Court 73 in the Royal Courts of Justice, where an annex has been set up to accommodate the hordes of journalists. The cost of the inquest has been estimated at £10m; £3m will be spent on security, which includes a police escort for each juror from their home every day.

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Why have we waited so long for this hearing?

Dr John Burton, the Coroner of the Queen's Household, ruled soon after the death that an inquest – which, under British law, must take place when a citizen dies abroad, suddenly or unnaturally – must await the outcome of inquiries by the French authorities, which took two years. Then Mr Burton's successor, Michael Burgess, commissioned a British police inquiry led by the Metropolitan Police Commissioner, Sir John Stevens, which took three more years.

There were further delays when Michael Burgess stepped down as coroner, citing an excessive workload. He was replaced by one of Britain's top judges, Baroness Butler Sloss, but she too resigned, in April 2007, after a higher court overturned her ruling that the inquest would sit without a jury and in private.

What did the two police investigations conclude?

After a two-year inquiry, a French judge said the driver of the princess's car, Henri Paul, was high on a cocktail of drink and prescription drugs. He was driving too fast as he tried to shake off photographers pursuing the car. But the judge cleared the paparazzi of manslaughter. An appeal was made against his ruling on the photographers but a senior court upheld his view in 2002.

The Stevens report last year agreed, saying that the driver was nearly three times over the drink-drive limit and driving too fast. He found no evidence of the conspiracy that they were murdered, as alleged by Dodi's father, Mohamed al Fayed, the owner of Harrods. It also dismissed a number of other dramatic claims that the couple were about to announce their engagement and that Diana was pregnant with Dodi's child.

What do the conspiracy theorists think?

Mohamed al Fayed insists his son and the princess were murdered by the royal family, in a plot orchestrated by Prince Philip and carried out by MI6 agents. The Establishment could not face Diana marrying a Muslim, he said. Diana herself, on at least one occasion, fed such notions, penning a note to her butler Paul Burrell in which she said "my husband is planning 'an accident' in my car".

Since then a whole publishing industry has sprung up to produce books with titles like Who Killed Diana?, Princess Diana: The Hidden Evidence and The Diana Conspiracy Exposed. They have fuelled all manner of theories, including that a white Fiat Uno, which has never been traced, forced the princess's car to crash in the tunnel, and that the chauffer's blood sample was switched at the mortuary.

Such ideas have wide currency. A poll for Sky News this week found that one in three people do not believe the death of Diana was an accident. It is, observed the latest coroner, Lord Justice Scott Baker, yesterday, "a subject upon which most members of the British public appear to have a view, often based on no evidence at all".

What are the unanswered questions?

Lord Justice Baker has already outlined 20 issues which will be addressed. These will include whether Henri Paul was really drunk or on drugs, whether the princess was pregnant, and whether she was fear for her life.

The inquest will also ask who was driving the white Fiat Uno which Lord Stevens confirmed clipped Diana's Mercedes shortly before it crashed. It will probe why the ambulance carrying Princess Diana took an hour and 40 minutes to get her to a hospital just four miles away and ask whether her life may have been saved had she undergone surgery more quickly. It will ask why Diana's body was embalmed, in contravention of French law, before it was flown back to the UK, making it more difficult to later carry out pregnancy tests.

Will the Queen testify?

Almost certainly not, though Mohamed al Fayed wants both her and the Duke of Edinburgh in the witness box. Lord Justice Baker has already rebuffed one demand by Mr Fayed's lawyers to get her to give evidence. Prince Charles may take the stand to clarify the evidence he gave to Lord Stevens. Diana's sister and executor, Lady Sarah McCorquodale, who represents the Spencer family, may testify. But Princes William and Harry will not be attending.

One of Britain's most formidable lawyers, Michael Mansfield QC, will represent Mr Fayed. Other barristers will represent the parents of Henri Paul, the Ritz Hotel, the Metropolitan Police, and there will be two barristers to defend the reputation of MI6. Major Jamie Lowther-Pinkerton, private secretary to Princes William and Harry, will be there on behalf of Diana's sons.

But the most headline-grabbing witness is likely to be the princess's butler, Paul Burrell. He was the man who, when accused of stealing the late princess's property, told his Old Bailey trial in 2002 that the Queen had warned him of "dark forces" at work in Britain, a revelation that caused the trial to collapse. He may air other confidences which could embarrass senior royals. Mr Fayed's legal team will press for the controversial "Squidgygate" tapes – of intimate phonecalls made by the princess to a lover – to be played to the inquest.

Will all this changeanything?

Almost certainly not. All the jury have to decide is how, where and when the couple died. Their verdicts can only be accidental death, unlawful killing or an open verdict. They have no authority to apportion blame.

But the testimony and documents from the inquest will be posted online and will feed the apparently never-ending Diana ferment. A recent poll suggests that less than a fifth of the population thinks the hearing will establish the truth about how Diana died. And only a third said they would accept the inquest verdict.

Some truths, it seems, are just too banal to accept. The idea that an inquest will calm the swirl of conspiracy seems remote. As does the wish of princes William and Harry that their mother be allowed to rest in peace.

Is the Diana inquest a waste of time and money?

Yes...

* Two official inquiries, in France and England, concluded the same thing – that Diana's driver, Henri Paul, was drunk and drove too fast

* There are better things for the public purse to do with £10m

* Another hearing will only add yet more fuel to the wild conspiracy theories

No...

* The inquest will offer the first chance to present evidence to a jury of ordinary citizens

* Witnesses like Paul Burrell may deal with areas which were only peripheral to the police inquiries

* It would have given scandal if the issue had been dealt swiftly with in private or with a jury from the Royal household