Police investigating the disappearance of Madeleine McCann are following a new line of inquiry which could see them carry out a series of searches in the next 48 hours.

The developments mark the first departure from investigations centred on Robert Murat, the only formal suspect in the case, who has been ruled out and will be cleared of his "arguido" status within weeks.

Every detective in the Algarve is on standby today. Search warrants have been signed and police are awaiting final orders to start an operation believed to be linked to a new potential suspect.

The Policia Judiciaria, the Portuguese equivalent of CID, has been on alert since Friday. The details of the lead are a closely guarded secret and detectives have been warned that they are being monitored for any leaks.

The warrants are only vaild until the end of tomorrow, but could be extended if police believe it is worth pursuing.

The Public Prosecutor's Office, which directs the police inquiry, signed a series of documents on Friday, ordering the PJ in Faro to put detectives on standby and authorising search warrants at locations that may be linked to the disappearance of Madeleine 109 days ago.

Staff from the Ocean Club complex, where Madeleine disappeared on May 3, will be also be re-interviewed today. A police source said: "We are re-interviewing several witnesses in order to clarify details that may be relevant to the new line of inquiry in light of facts we have found."

Pamela Fenn, 70, who lives in the apartment above where the McCanns were staying, and her niece, who is flying to Portugal from the UK, will be among those spoken to.

Mrs Fenn has said that in the weeks leading up to Madeleine's disappearance she scared off an intruder in her apartment.

There was no apparent sign of a break-in and it is thought the man may have had a key to let himself into the flat. She will be making a formal statement today at police headquarters in the city of Portimao. There was also another burglary in the complex a few weeks before in which police also suspected the intruder had a key.

Mrs Fenn's niece was staying with her aunt in the week that the McCanns were on holiday. She saw a suspicious-looking man hanging around the McCanns' apartment about the time Madeleine vanished.

She has spoken to British police and told them that he matched the description of a suspect seen leaving the scene with a child wrapped up in a blanket on the night of Madeleine's disappearance.

The police are working on the assumption that the four-year-old is dead, but that "strong theory" is not believed to be related to the new lead.

Unconfirmed reports in a Portuguese tabloid claimed that British police are also awaiting instructions from the Policia Judiciaria relating to an English resident.

Kate and Gerry McCann have still not been briefed on any developments but hope to meet detectives this week.

Over the weekend, friends suggested that the family would stay in Portugal until the end of the summer, pending developments.

The fighting fund launched to help the search has raised more than £1 million. The McCanns clarified this weekend that they are not using it to pay for accommodation.