McCanns' private detectives charging Find Madeleine fund £50,000 per month in EXPENSES

The Spanish agency Metodo 3 has racked up huge bills since it was appointed to the case in September and is charging them to the publicly funded appeal.

The costs are in addition to their £8,000 monthly fee, which is paid by one of the couple's millionaire supporters.

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Metodo 3's expenses are the biggest single cost to the rapidly dwindling fund, which raised £1.2million in public donations but is expected to run dry within months.

It was previously thought that the detective agency was hired for a flat, monthly fee of £50,000 for their services.

But the Mail can reveal today that it accepted a deal of £8,000-a-month, plus unlimited expenses to take on the high profile case, which has boosted its international reputation.

If its 'operational costs' top £50,000 then the excess is met by the McCanns' wealthy backers, who include double glazing tycoon Brian Kennedy and Virgin boss Sir Richard Branson.

Mr Kennedy is due to review Metodo 3's six-month contract before it expires next month, amid criticism that the agency has failed to find any solid evidence about what happened to Madeleine.

Its director, Francisco Marco, has also angered Mr and Mrs McCann with his public boasts that he was 'very close' to finding their daughter, and even that he hoped to return her to her family by Christmas.

The couple's spokesman Clarence Mitchell insisted the agency were 'doing valuable work on the ground'.

He confirmed the financial arrangements behind the six-month contract but insisted the £50,000-a-month from the fund was only used to cover 'legitimate operational costs'.

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Mr Mitchell said: "The monthly fee for their services is about £8,000.

"The £50,000 is for legitimate operational costs - having people scattered around different countries, hiring vehicles, hiring property to stay in and hotel bills.

"A private operation like this does cost money in terms of seeking information. It is something that needs that sustained level of funding to work. Private investigations are not cheap.

"The fund contributes £50,000 a month of publicly donated money because it's money to help find her. We feel that's proper use of that money."

Metodo 3 has claimed to have up to 40 agents working on the case in up to six different countries, including Morocco, Portugal and Britain.

It has been criticised for lavish spending, including moving its offices into one of the most prestigious streets in Barcelona in December.

But Mr Mitchell said the majority of the spending allowance went on travel, transport and accommodation for the teams of detectives.

He said: "People think it's £50,000 going straight into Francisco Marco's pocket, and that it's paying for them to move into plush new offices.

"Nothing could be further from the truth. They have taken this case on because it gives them a certain profile and prestige, not because it's going to make them rich.

"That money is used purely for legitimate operational costs and the fund is invoiced in full, as they would be for any expenses claim, which is effectively what it is. Their expenses are paid by the fund."

Metodo 3's involvement in the Madeleine case has proved controversial.

Five senior members of the firm, including Mr Marco, were arrested over a phone-tapping scandal in 1995 and accused of spying. The case was later dropped over claims of police entrapment, but they were also threatened with arrest in Portugal.

Under Portuguese law it is illegal for a private investigation to be carried out on a case that is being pursued by the police, and the agency was warned not to speak to police witnesses.

But Jennifer Murat, the mother of the first named suspect Robert Murat, has accused its detectives of bribing witnesses to change their accounts and has said she fears they are working to frame her expat son.

Mr Mitchell's comments that Metodo 3 has spent money 'seeking information' will fuel speculation that the agency has paid individuals for evidence.

Meanwhile, the McCanns, both 39, were said to be 'encouraged' by reports that their status as official suspects in the case will be reviewed after their friends have been re-interviewed.

Portugal's Attorney General Fernando Pinto Monteiro told the newspaper Expresso: "The couple's legal status will be considered at the appropriate moment, depending on various elements still to be obtained."

The newspaper reported that the McCanns would only remain as suspects if the new interrogations of their friends, the so-called Tapas Seven, revealed 'screaming contradictions'.