McCanns' lawyers combing Portuguese newspapers for 'black propaganda' by police

They hope to be able to prove that Portuguese officers detectives have been leaking negative stories about the McCanns in a bid to besmirch them.

The trawl will be overseen by Clarence Mitchell, the former Foreign Office official who was yesterday announced as the family's spokesman.

Mr Mitchell has been brought in to spearhead a new, more proactive stage of the McCann's fightback against allegations that they were involved in Madeleine's disappearance.

Since their return to Britain nine days ago, Gerry and Kate McCann have focused on building their legal case against the claims.

They spent all of last Friday and Saturday in consultation with their high-powered legal team, which is headed up by extradition expert Michael Caplan QC.

A spokeswoman for the family said that the couple are 'really pleased' with their lawyers and are working to 'get themselves into a strong a position as they can.'

She added: "They are being very pro-active. There may be different options for how the case may proceed. They will be working with their legal advisors to get in as strong a position as they can."

Though the spokesman refused to comment on the legal manoeuvres being considered it is understood that the McCanns are extremely frustrated by having to endure a slew of negative stories whilst they are themselves legally barred from commenting on the case.

If their defence team were able to prove the stories were deliberately planted by Portuguese police officers, it could help persuade a court - either in the UK or Portugal - that the couple have been 'set up'.

Gerry McCann has voiced his frustration on his internet blog, when he bitterly described the allegations against him and his wife as 'rumour, innuendo and wild speculation'.

Thanking the family's supporters for their messages of support, he added: "It means so much to us to know that so many people have not been deceived."

Clarence Mitchell quit his £70,000 a year post as the head of the Government's Media Monitoring Unit to work with the McCanns.

Confirming his move yesterday, he said: "They are an ordinary family caught up in extraordinary circumstances. I am utterly convinced they have nothing to do with the disappearance of their daughter.

"There are wholly innocent reasons for any of the so-called evidence that the police may or may not have. They are happy to explain those at an appropriate point.

"They are keen to make it plain that they have nothing to do with Madeleine's disappearance. But because of their legal situation they are constrained from commenting further."