Yet the millions spent on the long-running inquest which ended yesterday – and 2004's Operation Paget investigation into her death – may never silence those who believe the Princess's life was taken deliberately.

The initial cost of the inquest, which lasted more than 90 days and heard evidence from around 250 witnesses, is an estimated £3.6m but this figure is expected to increase as the Ministry of Justice has not yet received all of its invoices.

Other Government Departments are also facing substantial legal costs after they were represented at the hearing.

The Metropolitan Police have incurred estimated costs of £8 m for investigating the murder claims and for other services arising from the inquest, said a police spokesman.

This figure includes paying for the former Metropolitan Police Commissioner Lord Stevens's Paget inquiry into allegations of a conspiracy to murder Diana and her lover Dodi Fayed – reported to be £3.6m.

It also covers the legal team who represented the Metropolitan Police Commissioner at the inquest and police protection for the inquest jury.

Lord Stevens launched his Paget investigation in 2004 at the request of Michael Burgess, the Royal coroner, who was then overseeing the future Diana inquest.

But in December 2006 the former top policeman published his report, which rejected the murder claims that had been voiced by some, including Dodi's father Mohamed al-Fayed.

Inquest officials have already said that £2,885,618 was spent on the central London hearing between July 1 last year and February 29 this year.

A further £187,464 was incurred by Coroner Lord Justice Scott Baker and his predecessor Lady Butler-Sloss up to June 30 last year.

After February this year, the hearing sat for about a month at an estimated cost of more than £550,000, bringing the total inquest cost to date to £3.6.

But there are a number of major outstanding invoices.

Other Government departments with significant bills still to be paid include the Foreign and Commonwealth Office and Secret Intelligence Service, which were legally represented at the hearing.

The inquest has paid for a range of services, including providing video conferencing so witnesses could give evidence from countries including Nigeria and Australia.