Madeleine McCann case: Police trace phone records of people who were in Praia da Luz in 2007

Madeleine McCann: The girl was three when she was abducted during a family holiday in 2007

Police are attempting to trace mobile phones linked to 31 countries to identify thousands of people who were in the Algarve town of Praia da Luz when Madeleine McCann went missing six years ago, Scotland Yard said.

The scale of the huge trawl emerged as police said that they had identified 41 people of interest, including 15 Britons, during an investigation by the country's biggest police force after an appeal by the family to Home Secretary Theresa May in 2011. The girl, then aged three went missing from a holiday apartment on May 3, 2007 as her parents Kate and Gerry dined at a nearby tapas restaurant with friends.

“What we're trying to do is to use every route available to us to identify as many of them as possible and the phone data is one route into that,” said Detective Chief Inspector (DCI) Andy Redwood, the senior investigating officer on the inquiry. “If you were in Praia da Luz at the time, you may get a routine phone call from the police.”

The girl's parents are to make a new television appeal in light of “fresh, substantive” material unearthed as part of a British police investigation. In the week Crimewatch airs, equivalent programmes made in Holland, Germany and possibly Ireland, are expected to be broadcast.

Detectives have issued 31 international letters of request to mostly European countries in relation to some of the persons of interest as well as accessing phone records. A large but “manageable” list of phone numbers identified as being present in Praia da Luz - though not necessarily used to make phone calls - has been drawn up by detectives with a “significant” number unattributed to any named person.

And significantly, police officers are now able to create a log showing calls being made at the time of Madeleine's disappearance. Mr Redwood said his team could never say for certain that it knew everybody who was in Praia da Luz when Madeleine disappeared. He said 99 per cent of the phone numbers are likely to belong to “completely unaware and innocent individuals”.

Clarence Mitchell, the McCanns' spokesman, said: “Kate and Gerry remain very grateful to the Met for the work they are doing in liaison with the Portuguese authorities.

"Their forthcoming appearance on Crimewatch is an important stage in that ongoing process. Naturally, they hope it will lead to information that will provide the breakthrough to finding Madeleine."