Detectives hunting for Madeleine McCann have been ordered to prepare for an operation over the next four days that they hope will lead to a breakthrough, The Times has learnt.

The Public Prosecutor’s Office signed a series of warrants yesterday authorising searches at locations that may be linked to the disappearance of Madeleine 107 days ago. Officers have been told that the operation will be carried out by Tuesday.

The Portuguese Polícia Judiciária believes that it has uncovered evidence that could be significant in discovering what happened to Madeleine after she was taken from her bed in the Algarve resort of Praia da Luz.

The searches follow the arrival in Portugal of the result of tests on samples recovered from the McCann family’s apartment, their car and other locations in Praia da Luz.

The Times revealed on Thursday that the preliminary notes from the headquarters of the Forensic Science Service in Birmingham showed that traces of blood in the apartment had come from a man.

However, the findings received by the Laboratório de Polícia Científica in Lisbon on Wednesday indicated that the blood samples were too damaged to be checked against the DNA database of British sex offenders. Scientists have been attempting to recover a better profile.

The Portuguese magistrate in charge of the investigation has now been sent the full report on all the samples recovered as part of a review of the investigation completed with the help of British experts.

It is not known if the possible breakthrough in the investigation is connected with scientific evidence, although detectives are believed to have been monitoring the movements of at least one suspect for some time.

Police are also reported to have been reviewing two burglaries — one in the apartment directly above the McCanns’ apartment — which happened shortly before the family arrived at the Ocean Club resort.

Meanwhile, Madeleine’s twin sister and brother, Sean and Amelie, have finally been told that their elder sister is missing. They had previously been assured that she was on holiday and would be returning home soon.

Sean and Amelie, 2, were asleep in the ground-floor apartment when Madeleine was taken. Police have said that the twins slept throughout and have been unable to provide evidence.

Madeleine’s parents, Kate and Gerry McCann, have been advised by a British child psychologist on how to break the news to Madeleine’s siblings. The couple, both doctors, have been careful to maintain the twins’ daily routine but agreed last week not to take them to the usual morning sessions at the crèche of the Ocean Club resort because the presence of the media was disturbing other parents and children.

The twins, who, like Madeleine were born through IVF, have been encouraged to talk about their sister and her Cuddle Cat toy, which Mrs McCann now carries around wherever she goes.

Mr and Mrs McCann have thanked the thousands of people from around the world who have sent letters and e-mails of support. But the couple are still devastated at their daughter’s disappearance.

Mrs McCann, 39, a locum GP, recalled the pain of returning to Britain without Madeleine for a family baptism. “When we went back to the UK for a family baptism there was an empty seat on the plane and Sean said, ‘That’s Madeleine’s seat.’” she said. “Amelie asked me afterwards, ‘Where’s Madeleine? I miss my sister.”

The couple have also contemplated for the first time having to return home to Rothley in Leicestershire, without Madeleine. They have extended the rent on their villa on the outskirts of Praia da Luz only until the middle of next month.

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