Portuguese police initially investigated the disappearance, but Scotland Yard set up its own inquiry in 2011 and Operation Grange has since cost £11.1m.

A source close to the family, from Rothley, Leics, said: “They have never given up hope of finding out what happened to Madeleine, and still believe she could be alive. They appreciate everything the police are doing to get a resolution after all this time.”

The extra funding has approved by Prime Minister Teresa May, who met the McCann’s several times in her former role as Home Secretary.

The team of detectives searching for Madeleine was in September 2015 cut from 29 to four.

Sir Bernard Hogan Howe said nearly a year ago that police had one more line of inquiry to close.

He said: "There's been a lot of investigation time spent on this terrible case.

"It's a child who went missing, everybody wants to know if she is alive and if she is where is she, and sadly if she's dead then we need to give some comfort to the family.

"It's needed us to carry out an investigation together with the Portuguese and other countries have been involved.

"There is a line of inquiry that remains to be concluded and it's expected that in the coming months that will happen."