- 30 boxes of files handed over to Scotland Yard

- Agency followed leads in Spain and Morocco 

- Portuguese police criticised for closing case 

International investigation: Francisco Marco, head of the Metodo 3 agency, said his team followed leads worldwide

Scotland Yard detectives searching for Madeleine McCann are examining up to eight 'very important' new leads after meeting private investigators in Spain, it emerged today.

Yesterday four detectives visited the Barcelona headquarters of Metodo 3 - a Spanish agency that spent six months working for Madeleine's parents Kate and Gerry.

The British officers - from a 30-strong Metropolitan Police team carrying out a review of the case - took away around 30 boxes of documents compiled by the private investigators.

Afterwards the agency's director, Francisco Marco, said there were 'six, seven or eight very important leads' within the files that could help police locate Madeleine.

Mr Marco also criticised Portuguese police for failing to follow up those leads, and for shelving the Madeleine investigation.

He was a guest on the Spanish TV show The Ana Rosa Programme this morning, and said: 'We have provided (Scotland Yard) with all the documents and information we have collated worldwide about Madeleine's disappearance so they can continue the investigations we carried out in Spain, Morocco and the rest of the world.

'I think there are six, seven or eight very important leads in there.

Vanished without trace: Madeleine McCann disappeared from her bedroom in Praia de Luz, Portugal, in May 2007. Despite extensive efforts to find her, she remains missing

Still searching: Kate and Gerry McCann, at the launch of a book written by Kate, are not giving up hope

'They were passed at the time to Portuguese police who ignored them because it was a very politicised issue and they didn't want to look into anything that didn't come from their own sources... because of Portuguese chauvinism in this case, because they didn't want the English (police) or private detectives to discover more than they did.

'Every time anyone from Metodo 3 went to Portugal they were continually followed and monitored to see what they were doing.

'We were never allowed to do a proper job. Scotland Yard can now continue with all the work we did outside of Portugal and inside Portugal as well.

Dead ends: Convicted paedophile Raymond Hewlett, above left, died without talking to police, while another possibly Australian suspect remains unidentified

The English police are now continuing with an investigation which should never have been closed.'

Asked if he believed Madeleine was still alive, Mr Marco said: 'When we were investigating we were always trying to find a living child.

'I'm not going to answer your question because I don't want to offend the parents.

'Hopefully for the parents she will be found alive.

'I am a father, and to lose a child and not know where he or she is is the worst thing in the world.'

Crime scene: The holiday complex where the McCann family were staying when Madeleine went missing

Police files: Portuguese police photographed the room from where Madeleine was taken. But Mr Marco criticised the fact that they closed the case too early

Today Barcelona-based newspaper El Periodico de Catalunya published photographs of the Scotland Yard detectives, wearing suits, leaving the offices of Metodo 3, in the plush Eixample district of the city.

Metodo 3 were hired by the McCanns to look for their daughter in September 2007 - four months after Madeleine, days short of her fourth birthday, went missing during a family holiday in Praia da Luz, on the Algarve.

Metodo 3 were reportedly paid £50,000 a month to search for Madeleine and sent a team to Morocco to chase up leads that she might have been smuggled out of Portugal to north Africa.

Mr Marco was in daily contact with the McCanns, both doctors, from Rothley, Leicestershire, and claimed he had 40 staff working on the case.

In December 2007 he was criticised after claiming in a newspaper interview that he knew who had abducted Madeleine and would have her home for Christmas.

Metodo 3 continued to work part-time on the search for Madeleine after their six-month contract - funded by the McCanns' backer Brian Kennedy and the Find Madeleine Fund - expired.

Today Mr Marco said he still believed it was 'very possible' Madeleine had been smuggled out of Portugal to Morocco. He refused to go into further detail about the nature of the fresh leads.

Also included in the files taken by Scotland Yard are investigations the agency carried out into Raymond Hewlett, a convicted British paedophile who was in Portugal when Madeleine went missing and left for Morocco three weeks later.

Hewlett, an ex-soldier and convicted child rapist, died of throat cancer at the age of 64 in Germany last year having refused to talk to detectives about Madeleine's disappearance.

David Cameron asked the Met to examine all the evidence connected to the Madeleine case in July.

Scotland Yard detectives travelled to Spain last month to meet officers from the National Police and Civil Guard force.

They were also reportedly interested in chasing up a suspicious incident in Barcelona three days after Madeleine went missing.

A well-dressed woman with an Australian or New Zealand accent, described as looking like Victoria Beckham, is said to have approached a British tourist in the city's port area and asked him: 'Are you here to deliver my new daughter?'