Diana's funeral was estimated to cost nearly £5m

One memo said Diana and Dodi Al Fayed switched cars as they left the Ritz hotel in Paris to divert paparazzi.

But another said it was simply because their first car failed to start.

Another memo said the final cost of Diana's funeral was likely to be nearly £5m, a figure its writer remarked was "scarcely a deck on the Royal Yacht".

The papers, released by the Cabinet Office under the Freedom of Information Act, contain memos between officials and politicians, including Prime Minister Tony Blair, after the event.

A memo to Mr Blair dated the day of the crash - 31 August, 1997 - said the couple were "immediately subject to media attention" when they arrived at the Ritz and were surrounded by journalists when they left.

Official memos give differing views of why the couple changed cars

"They tried to leave quickly but the first hire car failed to start," the document, whose author is not revealed, said.

"The second car then left the hotel at speed. It travelled along a stretch of the river and entered the tunnel in which the car crashed."

The couple and driver Henri Paul, who was three times over the alcohol limit, were killed.

Another document signed "Jay" was sent on the same day to Foreign Secretary Robin Cook, who was in Singapore.

Sir Michael Jay was the ambassador to France at the time.

It said the pair left the Ritz in a different car "because, apparently, their getaway car failed to start, they got into another nearby car driven by a Ritz driver".

But a paper sent by Sir Michael to the Foreign Office a few weeks later, on 23 September, says the switch had been "a last minute change of plan aimed at diverting the waiting paparazzi".

I suspect something around £5m will be the final figure - scarcely a deck on the Royal Yacht Anonymous memo

In the days following the death, Mr Blair warned government ministers not to engage in any activities which "could result in political controversy".

Departmental concerns about the cost of Diana's funeral and who would pay began soon after her death.

One anonymous memo said "the Treasury have been pretty good so far, but the bill, which stands at around £3m, is mounting".

However, the author adds: "I suspect something around £5m will be the final figure - scarcely a deck on the Royal Yacht."

This was in reference to the government decision to decommission Britannia, which was costing £9m a year to run.

However on the same day, Hayden Philips, Permanent Secretary at the Department of Culture, Media and Sport, said in a separate document that the department had "no financial cover" for the event.