Detectives investigating the disappearance of Madeleine McCann are still considering whether she was kidnapped, the detective leading the inquiry indicated last night.

Paulo Rebelo, one of Portugal’s most senior detectives, was speaking after 80 suspected paedophiles were arrested in the country’s biggest-ever child exploitation operation.

Portuguese detectives were last night beginning to sift through the tens of thousands of files found on the 150 computers seized during the raids.

The new impetus will be welcomed by Kate and Gerry McCann, who have been official suspects for more than a month. They have appealed for officers to resume the search for their daughter.

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Last night Mr Rebelo said that “all lines of inquiry remain open”. The Times reported yesterday that British police had been asked to take DNA samples and fingerprints from all holidaymakers at the resort where Madeleine disappeared after Portuguese detectives found evidence of a possible kidnapper.

German and Dutch police are also believed to have been asked to trace and interview guests who were staying at the Ocean Club resort in Praia da Luz on May 3.

On Tuesday a team of Portuguese detectives visited the ground-floor apartment where the McCanns stayed to take measurements for a detailed reconstruction of events. They were said to have been particularly interested in the small service area beneath the apartment.

The apartment has not been occupied since the beginning of August after a British sniffer dog reportedly signalled that it might have discovered traces of a corpse.

Senior officers suspect that Mr and Mrs McCann were involved in Madeleine’s disappearance, but a Portuguese judge has told them that there is not enough evidence to demand that they return to the Algarve for further questioning.

A source close to the investigation told The Times: “One of the things they want to do is clarify all the problems so if they want to advance on the McCanns there will be no unanswered questions. They are certain that Madeleine died in the apartment but the question they cannot answer is who took the body and where it went.”

Mr and Mrs McCann said yesterday that they were considering legal action after claims that tests on samples of Madeleine’s hair proved that she had been drugged before she disappeared. The couple, both doctors, said that they had never used sedatives on Madeleine or their two-year-old twins, Sean and Amelie.

The newspaper 24 Horas reported that scientific evidence analysed by both Portuguese and British experts suggested that all three children had been drugged. Portuguese detectives investigated the possibility of sedation because Madeleine did not cry out on the night that she vanished and the twins continued to sleep as the search for their sister was carried out.

Clarence Mitchell, spokesman for the McCanns, said: “Gerry and Kate McCann wish to make it categorically clear that they have never, ever, used sedatives on their children.

“Lawyers for the McCanns will be monitoring British coverage of this particular allegation and will not hesitate from taking action at the appropriate stage where necessary.”

The Forensic Science Service has tested dozens of samples recovered from the apartment, a car hired 25 days after Madeleine disappeared and other vehicles and properties at its laboratory in Birmingham.

Mr Rebelo took charge of the investigation on Monday after the previous head was demoted for claiming that British police were being manipulated by the McCanns.

The team is now down to six from the hundred officers assigned to the case when Madeleine first went missing.

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