BRITAIN'S top policeman has said that missing Madeleine McCann could still be found alive.

And Metropolitan Police commissioner Sir Paul Stephenson hit out at recent criticism after PM David Cameron asked Scotland Yard to look into the case.

Sir Paul said Met officers occasionally helped out other forces, including a search two years ago in Jersey for people who had been missing for 30 years.

He said: "One of them was found alive. So, you know, there is a remote chance."

Sir Paul said senior officers had already started work on the case and he took the request "very seriously".

He said: "This is not unique. I do think this is probably a case that would benefit from a review.

"We do review these sort of cases and there may be some benefit here and 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."

Madeleine went missing shortly before her fourth birthday from a holiday apartment in Portugal on May 3, 2007.

Portuguese police, helped by officers from Leicestershire police, launched an investigation.

But no police force has been actively looking for Madeleine since 2008.

Cameron stepped in after a plea by parents Kate and Gerry McCann, of Rothley, Leicestershire, to revive the hunt.

Sir Paul added that the Yard had helped authorities in Antigua investigate the murders of British honeymooners Ben and Catherine Mullany in 2008 and they had also reviewed the "dreadful Soham murders".

He said: "We are lending our expertise following a request and with appropriate funding.

"I think, on balance, it is the right thing to do. We are currently looking at the scale of the task."

Members of the Metropolitan Police Authority last week hit out at Cameron's move, saying the money spent on a case review could be used better elsewhere.

Kate recently released a book about Madeleine's disappearance.