Madeleine McCann on holiday in Portugal in 2007

BRITAIN’S top policeman has agreed to join the hunt for Madeleine McCann because he believes she may still be alive, he revealed yesterday.

Metropolitan Police Commissioner Sir Paul Stephenson defended his decision to reopen the case, insisting there was “always a chance” it could lead to Madeleine being reunited with her parents.

Critics had branded the new investigation a “ludicrous” waste of money which would tie up police resources while denying justice to other victims of crime.

Sir Paul agreed to carry out a review following a request from David Cameron.

The Prime Minister stepped in after a heartfelt plea from Madeleine’s parents, Kate and Gerry McCann from Rothley, Leics.

A formal request was made to the police chief by Home Secretary Theresa May who pledged the operation would be funded by the Government.

In a radio interview Sir Paul yesterday said it was not unique for his officers to be called in to assist with difficult to solve cases abroad.

He highlighted the murders of British honeymooners Ben and Catherine Mullany in Antigua in 2008. A team of detectives flew to the Caribbean island to help bring the couple’s killers to justice.

Sir Paul said: “There is always a chance. When you receive a request, supported by the Prime Minister, from the Home Secretary, you take that very seriously.

“This is not unique. On balance, I think it was the right thing to do. We do review these sort of cases and I think there may be some ­benefit here.”

He admitted some trails will have gone cold. But he added: “We will lend our expertise, with the Portuguese authorities staying in the lead. It will go to our homicide team and people who are used to doing reviews.”

Sir Paul said senior officers had already started work and would go through all documents in the case.

The review is being led by cold case expert Detective Chief Inspector Andy Redwood from the Homicide and Serious Crime Command.

The McCanns have welcomed the review.

Madeleine vanished from their holiday apartment in Praia da Luz, Portugal, on May 3, 2007, just days before her fourth birthday.

The couple claim vital clues were missed during a shambolic investigation by Portuguese detectives, which was shelved in 2008. Since then, no police force has been actively ­looking for Madeleine.

Last week Metropolitan Police Authority member Jenny Jones said: “It is ludicrous. This could take years and will cost millions. It is very unusual for police to step in like this and it is not an appropriate use of police resources.”