The Princess, 36, and her lover Dodi Fayed, 42, died on August 31, 1997, when the car they were travelling in hit a pillar in a Paris underpass. A French investigation blamed the driver, Henri Paul, for drink-driving at high speed.

Lord Steven's investigation into their deaths, which has focused on allegations that she was murdered, will be revealed tomorrow at a press conference in central London.

It is widely expected to agree with the French findings that the Princess died in an accident that was caused by excessive speed after the driver lost control of the Mercedes.

The report is also expected to dismiss claims that the Princess was engaged to Dodi Fayed, or even pregnant by him.

The British police inquiry has examined a number of conspiracy theories surrounding their deaths, including that the couple were murdered in an MI5 plot - something claimed by Mohamed al Fayed, the Harrods boss.

The inquiry, which has cost more than £2.5 million and taken three years to complete, is said to bring together 20,000 documents and 1,500 witness statements.

It is the first examination in Britain of the events which happened in the Pont de l'Alma tunnel in Paris almost a decade ago.

The Princes were to be briefed on its findings today - soon after hearing that the first batch of tickets for a concert they are organising to mark the tenth anniversary of their mother's death sold out within minutes.

Tickets for the 'Concert for Diana', to be held at the new Wembley Stadium next year, appeared on eBay this morning priced at up to £300 per pair. The face value is £45.

One pair of tickets drew 19 bids in just over an hour.

But, the internet auction site immediately banned them from sale "out of respect".

A message placed on the website today read: "In view of the unique and commemorative nature of the Concert for Diana event and as a mark of respect for the memory of the late Diana, Princess of Wales, we've decided to prohibit the resale of tickets to this event on the site. Any tickets currently listed will be removed as soon as possible."

Famous names who will be starring in the concert on July 1 next year include the Princess's favourite group Duran Duran, and the singer Joss Stone.

Sir Elton John also features in the line-up, raising speculation that he may perform a version of Candle in the Wind, which he sang at the Princess's funeral in 1997. Sir Elton had vowed he would never play the song again unless asked by the Princes.

As well as the concert, a church memorial service will be held for the late Princess.

The findings of the Stevens report will form part of the inquest into the deaths of the couple, being overseen by Dame Elizabeth Butler-Sloss. The former top judge, who already has a copy of the inquiry report, is holding the preliminary hearings in January in public which will determine whether there will be a jury that would be made up of members of the Royal household.

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