Madeleine McCann lead: Cops track widow as key witness

Madeleine McCann (pictured), then three, vanished in May 2007 while on holiday with her family in Portugal. Photo / Supplied

Officers believe a widowed woman - thought to Eastern European - could hold the key in the search for Madeleine McCann.

Detectives were given extra funding to trace a 'critical witness' who is missing from Portugal, the MailOnline reported.

The sought-after woman is believed to have lived near the holiday flat in Praia da Luz on the Algarve, from which Madeleine vanished in May 2007, before leaving the country after her husband died.

An extra $283,000 was added to Scotland Yard's $22 million Operation Grange to find Madeleine in order to track down the woman.

"She may have seen or heard something which to her may seem insignificant but to us could prove vital. If she recognises herself she should contact police. She has nothing to fear. This is just to eliminate her from inquiries," a source told The Sun.

Madeleine McCann (pictured), then three, vanished in May 2007 while on holiday with her family in Portugal. Photo / Supplied

A further source told the newspaper that Operation Grange, launched in 2011, described the woman as a "critical line of inquiry'.

Police still believe that Madeleine may have been taken during a burglary that had 'gone wrong'.

Her parents Kate and Gerry insist they must continue as there is 'absolutely nothing' to suggest their daughter has been harmed.

Not one piece of forensic evidence linked to the little girl has been found since she vanished from her family's Praia da Luz holiday apartment.

Her parents Kate and Gerry (pictured) insist they must continue as there is 'absolutely nothing' to suggest their daughter has been harmed. Photo / AP

And despite trawling through thousands of tip-offs and potential sightings, police have not confirmed that a single one was her.

Last year, then-commissioner of the Metropolitan Police Sir Bernard Hogan-Howe said the squad was expecting to mothball their work within months.

It is understood police chiefs have a working theory on what happened to Madeleine but may be unable to reveal it publicly because it implicates an individual or individuals.

The Portuguese investigation of Madeleine's disappearance was criticised by the British authorities as being not fit for purpose. Scotland Yard began an investigative review into the disappearance in 2011, on the orders of then-Prime Minister David Cameron.

However, The Sunday Times understands Met detectives have been relying on Portuguese transcripts of key interviews with British witnesses, rather than conducting their own.

Operation Grange has conducted no formal witness interviews with Gerry or Kate McCann or the seven friends they dined with on the night Madeleine disappeared.

Speaking a few weeks ago, a spokesman for the family said the McCanns remain 'extremely thankful' to police for requesting extra funding.

Madeleine had been left alone sleeping with her younger twin siblings while her parents were dining in a nearby tapas restaurant. Photo / Getty

Their representative, Clarence Mitchell, said: "They are very encouraged there remains work to be done that requires them seeking an extra budget.

"They are grateful to all those officers who are still working on the case and are actively looking for Madeleine.

"They appreciate everything the police have done and are doing to get a resolution after all this time."

Scotland Yard has insisted it will not reduce the small team left on the case any further as the "inquiry has not reached a conclusion".

- Additional reporting by NZ Herald