A Scotland Yard detective has revealed that they are investigating 38 people in connection with the disappearance of Madeleine McCann. Madeleine, from Rothley in Leicestershire, disappeared while on holiday in Portugal in May 2007.
Speaking at Evelina Children's Hospital in London today during celebrations of the 65th birthday of the National Health Service, Mr Cameron said: "It is welcome because they say that there is new evidence, new leads to follow, new things to be done.
"It was a case that did shock and still shocks the nation and if an answer can be found we should try and find it."
The Metropolitan Police said yesterday that detectives had identified 38 people of interest including 12 UK nationals following a two-year review of evidence in the case.
The Met Police said there are 38 people of interest in the Madeleine McCann case. Here is a timeline of the key events in her disappearance.
What happened to Madeleine? It is likely only one person knows the answer, and finding that person is the focus of a British investigation.