The four-year-old disappeared on 3 May while her parents ate at a nearby tapas restaurant.

The couple from Rothley have said they were taking turns to regularly check on the children.

Kate discovered Madeleine had gone missing at about 10pm and it is understood that Gerry checked on the three children at about 9.05pm.

A family friend said: "He believes there was certainly something odd. The bedroom door was ajar when he got in and he thought: 'That's strange'.

"He went into the room, checked that Madeleine was still asleep in bed; she was and he came out and closed the door. Initially, he thought that she might have got up and gone to the toilet or gone to get a drink or something but now he thinks that the abductor must have been in there hiding."

The friend said Gerry believes the abductor came in, opened the door and did not have time to close it as he went to hide when Gerry arrived.

"Once Gerry had left he would have known he had to come out very quickly and because Gerry went out through the patio door, he went out through the window, " said the friend.

"He has no proof but that is what he believes."

It is believed that when Kate went to check on the children a gust of wind in the room caused the door to slam behind her. She then realised the bedroom window was open and Madeleine was gone.

The family's spokesman, Clarence Mitchell, has dismissed claims that the McCanns are hiding behind their right to silence, which is granted to them as 'arguidos' or formal suspects.

He was responding to the reported comments of Carlos Anjos, president of the ASFIC, Portugal's equivalent of the Police Federation.

The Portuguese newspaper Diario de Noticias claims he said it was a "difficult and complex investigation made worse by the stance of the McCann parents who do not facilitate or help the investigation".

Mitchell said: "We are not prepared to comment on Mr Anjos's remarks but Kate and Gerry have always said they are willing to return to Portugal at any time to help the police with their investigations."