Police searching for Madeleine McCann last night issued a detailed description of a possible suspect who was seen on the night the four-year-old disappeared.

The man, who is white and between 35 and 40, was seen walking in the area of Praia da Luz, Portugal, at around 9.30pm on May 3. The Policia Judiciaria said that he was "carrying a child or an object that could have been taken as a child".

Chief Inspector Olegario Sousa said the man was 5ft 10in, of medium build and was wearing a dark jacket, light beige trousers and dark shoes. He urged anyone who had seen him to come forward to police.

Mr Sousa added that dozens of reports of Madeleine's possible whereabouts were still being checked, but none had proved positive. "The investigation is ongoing," he added.

A source indicated last night that the sighting of the man was made by a friend of Gerry and Kate McCann, who was with the couple's party in Portugal.

It is thought that the police have known about the sighting for three weeks but have not released the description because of Portugal's strict "secret of justice" laws which forbid the disclosure of information about an investigation.

The decision to issue a description of the man had to be sanctioned by the public prosecutor. It followed an "amicable" meeting between senior Portuguese police and the McCanns, which is believed to have taken place on Thursday. The couple also had discussions with British Ambassador John Buck and UK police.

A spokesman for the McCann family welcomed the release of the description and said Madel-eine's parents were pleased that there "appeared to be a new development".

Earlier yesterday, Mr and Mrs McCann spoke of their feelings of guilt at not being there when Madeleine was abducted from the family's holiday apartment.

In their first interview since she vanished three weeks ago, they said that in the first few days after she was taken they had blamed themselves. The couple were eating in a tapas bar at the Ocean Club Resort in Praia da Luz and were regularly checking on their three children when Mrs Mc-Cann discovered her daughter was missing.

The couple said that the resort was "very safe" and dining out in the restaurant within the grounds was "no different from having dinner in the garden".

Mr McCann, who is originally from Glasgow, added: "I think it's fair to say that the guilt that we feel, having not been there at that moment, irrespective of whether we had been in our bedroom or not, will never leave us."

Mrs McCann, who was holding her daughter's favourite pink toy throughout the interview, said: "Certainly in the first few days I think the guilt was very difficult. But I think as time goes on you feel stronger."

Meanwhile, British specialists have flown to the Algarve to re-examine the abduction scene.