POLICE in Portugal investigating the disappearance of Madeleine McCann have conceded that the trail is going cold.

Inspector Olegario Sousa, the police spokesman in the case, said that a lack of physical evidence had slowed down the investigation.

Madeleine vanished from her hotel bedroom in Praia da Luz almost four months ago. Mr Sousa said the investigation was "a complex, difficult case, where we have to try and reconstruct what happened largely on the basis of witness statements by asking people what happened".

He continued: "Even if we suspect someone, we still need hard evidence to prove our case. Time is our enemy."

Yesterday, a friend of Madeleine's parents said smears published about him in Portuguese newspapers were "completely untrue and extremely hurtful".

Russell O'Brien, 36, was among the group the McCanns were dining with on the night that Madeleine went missing.