Police say 18 potentially linked cases involve a male intruder going into villas occupied by British families on holiday in Portugal’s Algarve region between 2004 and 2010.
Some of those involved sexual assaults on children and little or nothing was stolen.
Madeleine was reported missing in May 2007, when she was aged three, from her family’s resort apartment in Praia da Luz on Portugal’s south coast.
Her disappearance remains unsolved. Last month police said a suspect may have been responsible for 12 cases of intrusions and assaults on children in the Algarve. Police said yesterday further inquiries have identified six more cases.
They include nine sexual assaults, three near-misses and six incidents where the intruder was disturbed.
Detective Chief Inspector Andy Redwood said yesterday: “We have now identified a further five sexual assaults and one near-miss. None of those six matters we were aware of prior to our appeal.
“In this new tranche of information, we have got one crime which is very clearly in the heart of Praia da Luz in 2005, on a young, white, ten-year-old girl. Clearly, the fact that we’ve now got an assault that is in the heart of Praia da Luz, very close to where a previous matter had been reported, means that we are even more interested in this as part of the inquiry.”
Officers are now poised to stage operations on Portuguese soil. Investigators from Scotland Yard are waiting for an official agreement later this week, and hope to begin “operational activity” linked to the case in the near future.
Deputy assistant commissioner Martin Hewitt said: “I am cautiously optimistic that in the not-too-distant future we are going to start to see activity.”
Mr Hewitt would not reveal what the joint operations will involve.
British detectives launched a fresh investigation into Madeleine’s disappearance in July last year – two years into a review of the case.
In the previous appeal, the suspect was described as a tanned, dark-haired man who spoke English slowly, with a foreign accent and possibly slurred speech, had unkempt hair was unshaven, and smelled strange.
Some witnesses said he had a pot belly.
In six of the offences, the man sat on or got into bed with young girls.
Even when he was disturbed, witnesses said that he remained calm.
In two of the break-ins, he was wearing a distinctive burgundy long-sleeved top, which some witnesses said had a white circle on the back.
There is a £20,000 reward for information leading to the arrest and prosecution of those responsible for Madeleine’s disappearance.
After shelving their inquiry into Madeleine’s disappearance in 2008, Portuguese authorities said last October that a review had uncovered enough new information to justify reopening it.
Portugal has declined to set up an official joint investigation with the Met.
Mr Hewitt said Prime Minister David Cameron and Home Secretary Theresa May have expressed a personal interest in the case, and stand ready to intervene to press the Portuguese authorities for help if necessary.