Scotland Yard detectives have arrived in Portugal to oversee the excavation of a number of sites as part of the investigation into the disappearance of Madeleine McCann.

The digs for evidence are to take place at several locations in the resort where the youngster vanished in 2007.

Forensics officers are due to use ground penetrating radar equipment to aid the search at three sites in Praia da Luz.

Madeleine disappeared from the apartment she was staying in with her parents and two siblings on May 3, 2007. She was three years old at the time.

Officers from the Metropolitan Police have also identified three potential suspects they want to talk to, not necessarily around Madeleine's disappearance, but who had been involved in break-ins in the area.

However, they have reportedly been refused permission by Portuguese authorities to search the homes of these burglary suspects, who used to work at the Ocean Complex at the time Madeleine vanished.

Sky's Crime Correspondent Martin Brunt, in Praia da Luz, said: "That's a blow for Scotland Yard." 

He said disagreements over leaks to the media may delay British police in their efforts to scour areas they will be given access to. 

"I'm not sure that those searches are going to begin quite so quickly," he said.

"The Portuguese are making it very clear that they were not happy with journalists being briefed. It's not something that happens in this country and in fact, the Portuguese authorities, according to the Scotland Yard message last night, had threatened to stop any of the work once it begins if they hear that Scotland Yard are talking to reporters, or indeed if reporters are in any way disrupting the work.

"I get a sense that because of this developing row, that may put off what is going to happen soon, but maybe not in the next couple of days as we anticipated."

Kate McCann told Sky News last week, on the seventh anniversary of her daughter's disappearance, that she needed to know what happened - even if it was the "worst-case scenario".

"Madeleine's either alive or she isn't and we can't change that."