“She might look different, she could be speaking a different language, she might have her hair different, she might have different interests but, you know, she’s still our daughter.”

Kate and Gerry McCann were also interviewed by US chat show host Oprah Winfrey as part of a series of high-profile television appearances to mark the second anniversary of Madeleine’s disappearance.

In a statement issued ahead of yesterday’s anniversary, the McCanns said: “It is two long years since Madeleine was taken. It is two years since we were a happy family of five.

“The pain and anxiety does not lessen, but our determination to find our beautiful daughter remains steadfast.

“We are no longer looking for a four-year-old little girl – but a six-year-old one. This is crucial.

“We are hoping that the new, age-progressed image of Madeleine, aged six, produced by the National Centre for Missing and Exploited Children in Washington, will help people to see what Madeleine may look like today.”

The documentary, Cutting Edge: Madeleine Was Here, follows ex-Cheshire detective Dave Edgar and former Merseyside detective Arthur Cowley as they try to piece together what eye-witnesses say happened two years ago.

The detectives have looked through 30,000 files of information released by Portuguese police about their investigation when the case was shelved last summer.

Speaking publicly about the inquiry for the first time, the two former police detectives say the “answer still lies” in that small section of the Portuguese coast.

Mr Edgar said: “There’s someone local, lives locally, who has the answer to this, and not, you know, much wider than 10, 15km away from Praia da Luz.”