The parents of Madeleine McCann have asked Portuguese police to question 25 witnesses whom they believe hold the key to solving the mystery of their daughter’s disappearance.

A list of names submitted by lawyers acting for Kate and Gerry McCann include the seven British friends who were dining with the couple when Madeleine was taken from the Ocean Club resort in Praia da Luz on May 3.

Employees at the resort, including the crèche nannies who had looked after Madeleine, are also on the list. A source close to the McCann’s legal team said: “Mr. and Mrs. McCann have always said that they and their friends are prepared to do whatever it takes to find Madeleine. These people can prove that Madeleine’s parents could not have been involved in her abduction and could provide evidence about who took their daughter.” The couple have the legal right to request police operations since they were made arguidos, or official suspects.

Portuguese detectives are expected in Britain imminently after formally requesting to re-interview at least four of the seven British friends who were in Praia da Luz with the McCanns. All seven could now be interviewed after the McCann’s request.

The friends could ask to be made official suspects before the interviews so that they have the right to have a lawyer present during the questioning.

The interviews had been expected to be carried out last month but were delayed while the Portuguese police and a public prosecutor studied the results of forensic science evidence and carried out a reconstruction of events.

The McCann's, from Rothley, Leicestershire, have been told by British police liaison officers that the Portuguese police are “reviewing” the case against them.

Paulo Rebelo, the new head of the investigation, has told his officers to consider all possibilities, including that Madeleine might have been abducted by a stranger.

The couple’s Portuguese lawyers have applied to see the details of the evidence against them but this is set to be rejected after the other official suspect, Robert Murat, had a similar application dismissed by the Court of Portimão last week because of the complexity of the case and the media interest.

Gerry McCann wrote on his blog to mark the six months since his daughter’s disappearance: “We have no idea whether she is suffering but we have to hope and pray that she is being treated like a princess, as she deserves.” McCann intends to resume full-time work in January as a consultant cardiologist at Glenfield Hospital, Leicester.