The parents of Madeleine McCann are to make a television appeal in light of "substantive" material uncovered by a fresh British police investigation.
Kate and Gerry McCann will appear live in the studio on the BBC's Crimewatch on Monday to present "different material" on the case.
Scotland Yard is for the first time trawling through a vast log of mobile phone traffic identified in Praia da Luz, in Portugal, at the time of Madeleine's disappearance.
Madeleine went missing in 2007
The McCanns will appear live in the studio during an episode of BBC Crimewatch on Monday October 14, which will also feature a reconstruction and pre-recorded interviews with the couple.
Describing the programme, Assistant Commissioner Mark Rowley, of the Metropolitan Police, said: "It's substantially different. It's not just a bland 'can you help us' appeal, there is some different material and a different understanding to be presented."
And Scotland Yard has revealed that since launching its own investigation, 41 people of interest have been identified, including 15 UK nationals, up from 38 people of interest including 12 UK nationals established in July.
Detectives have issued 31 international letters of request (ILOR) 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.
Asked if this move could be key to the investigation, Detective Chief Inspector (DCI) Andy Redwood, the senior investigating officer on the inquiry, said: "It could be."
He added: "We've got a data set of phone traffic. Within that phone traffic you can see we've got some of those numbers we can attribute to people, but a large number of them we can't.
"So in a targeted way, we're trying to say in a particular moment in time, that is around the moment of opportunity, who's there. It's really as simple as that."
He went on: "A lot of the focus is not necessarily to find a suspect, but also witnesses. We're trying to understand who was there for a range of reasons."
Mr Redwood said his team could never say for certain that it knew everybody who was in Praia da Luz when Madeleine disappeared.
He went on: "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, as are appeals. If you were in Praia da Luz at the time, you may get a routine phone call from the police."
Mr Redwood said the phone data shows a timeline with "calls made and where they went to as a running log".
He said 99% of the phone numbers are likely to belong to "completely unaware and innocent individuals".
Portuguese Police already had access to the list of phone numbers but it has not previously been as closely scrutinised.
In the week Crimewatch airs, equivalent programmes made in Holland, Germany and possibly Ireland, are expected to be broadcast.
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."
Mr Rowley added: "It's important to stress, the Crimewatch appeal is not simply 'this is a live investigation has anyone got any information?'. It is more than that.
"There is new information not previously presented. Fresh, substantive material upon which to make an appeal.
"It will be a substantive and substantial programme rather than a broad implication that people can help us."
Madeleine went missing from a holiday apartment as her parents Kate and Gerry dined at a nearby tapas restaurant with friends.
The Portuguese investigation officially closed but authorities there are backing the Scotland Yard inquiry and officers from both countries will work together in pursuing new leads.
The Scotland Yard investigation, which started as a review, has amassed 39,148 documents, of which 21,614 have been processed, relating to information from Portuguese Police, eight private investigators and other British forces, such as Leicestershire Police.
It now has a team of six Portuguese detectives based in Faro, who are carrying out inquiries on Scotland Yard's behalf.
The McCanns are currently suing former police chief Goncalo Amaral for libel over claims in the book The Truth Of The Lie.