Kate McCann has spoken of her continuing pain over missing daughter Madeleine and how she wants to know what happened even if it is the "worst case scenario".

McCann, who with husband Gerry has been looking for her daughter for seven years since she went missing in a Portuguese holiday resort, said: "I'm not underestimating the blow of hearing bad news that your child had been killed, because obviously we're not going to go, 'OK at least we know.'

"But I've spent hours thinking about that and, each time, I still come up thinking we need to know. Regardless we need to know."

"But there is always the worst case scenario. That's always been a possibility."

Madeleine, then three years old, vanished from her bed in the resort of Praia Da Luz in the Algarve in 2007 and the global hunt for her has never let up.

Police recently issued a fresh appeal for information about a man wearing a burgundy top with a distinctive red and white SuperBock logo on it. The suspect is believed to have carried out a string of break-ins and sexual assaults on young girls in the area in the months before Madeleine vanished.

Kate said the family was braced for the possibility that efforts to find Madeleine alive may yet prove fruitless.

"Anyone who thinks that we're blinkered doesn't know us," she said.

McCann was speaking at the launch of a new email and texting service for spreading the word when a child goes missing. Called Child Rescue Alert, it is open to the public. Messages are sent to registered users by police containing details about a missing child.

McCann said: "When a child is abducted, families are devastated and entire communities are torn apart. The agony of not knowing where your child is is almost impossible to imagine. The helplessness is at times overwhelming.

"But there is now something we can all do to help. Please sign up to receive alerts - you could save a child's life."