Detectives investigating the disappearance of Madeleine McCann are preparing to travel to Britain to carry out further inquiries, amid concerns that her parents are under an intolerable strain.

Police in Portugal have already been authorised to carry out a series of searches in Praia da Luz and to reinterview key witnesses as they attempt to build a case against Kate and Gerry McCann. A team of Portuguese officers will travel to Leicester to work alongside British officers who are investigating the McCanns.

Two senior Portuguese officers, Guilhermino Encarnação, the director of the PolÍcia Judiciária in Portimão, and Gonçalo Amaral, the co-ordinator of the force, had a three-hour meeting yesterday with Pedro Daniel dos Anjos Frias, the criminal instructional judge who is reviewing the evidence in the case, ahead of plans to order Mrs McCann to return to the Algarve for further questioning.

The Times has learnt that the couple will not be returning to the Algarve until next Wednesday. The judge has a deadline of Thursday to consider requests from the public prosecutors for a series of searches.

Madeleine McCann: the key questions

Why are the "Tapas 9" key to solving the Madeleine mystery?

Related Internet Links

• The latest full coverage of Madeleine McCann

BACKGROUND

• McCanns consider interview bids

• Madeleine McCann: the global reaction

• The forgotten victim in the McCann case

Multimedia

• Pictures: searching for Madeleine

• Video: McCann family start holiday

Related Links

• Experts try to unlock DNA clues

• Q&A: Why is hire car the key in prosecution?

Portuguese police are said to believe that they will never find Madeleine’s body, making it difficult to secure a conviction. Investigators think that her body was most probably dumped in a bag weighed down with stones and thrown off a British-owned yacht on the high seas, according to reports in the Diário de NotÍcias newspaper.

The police case against the McCanns includes traces of Madeleine’s body fluids and hair allegedly found in their holiday apartment in Praia da Luz and in a car that was rented by the couple 25 days after her disappearance. Reports have suggested that the finding of Madeleine’s DNA in the boot proves that her corpse had been in there. Officers also believe that there are inconsistencies in statements made by the couple and a group of friends whom they were with on the night she disappeared.

But a senior detective involved in the investigation said that although officers had plenty of circumstantial evidence, they could not prove what happened to Madeleine and had “nothing concrete”, a Portuguese newspaper has reported. The detective, spoken to by 24 Horas, a Portuguese newspaper, said: “Even if the blood and the traces gathered in the car and the apartment were confirmed to correspond 100 per cent with the little girl’s DNA that would prove nothing.”

It was also reported yesterday that the Forensic Science Service in Birmingham had discovered evidence from Madeleine’s hairs that she had been regularly sedated, leading to the suggestion that she might have been killed by an overdose. The couple have denied sedating Madeleine.

Mr and Mrs McCann met their lawyers and media advisers in London yesterday to discuss how to respond to accusations that Madeleine was killed accidentally.

Times Recommends

• Please help: maimed children of war want their lives back
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president