Kate and Gerry McCann are prepared to take a lie detector test to clear their names.

The couple are so confident of their own innocence that would take the polygraph test in Portugal, a source close to the couple said.

Relief: The McCanns visiting their lawyers in London yesterday

And new details have emerged about the sighting of the "mystery man" the McCanns believe was their daughter's abductor.

For the first time, a friend of the couple claimed the stranger seen walking away from the Praia da Luz holiday complex on May 3, apparently with a child in his arms, was heading towards former chief suspect Robert Murat's home.

The McCanns' offer to submit to lie detector tests would only serve to help clear any public doubts about the McCanns' guilt or innocence, as polygraphs are inadmissible in Portuguese courts and are never used by Portuguese police during the course of investigations.

The source said last night: "If they were asked to take a lie detector test, of course they would agree.

"Kate and Gerry are happy to do anything that would help clear their names."

Arguidos: Madeleine's parents, pictured after intense questioning by Portguese detectives in Portimao, say they'll take lie detector tests to clear their names

Any significant difference in these rates as the subject gives answers to different questions, may indicate that the subject is lying.

The McCanns yesterday announced the appointment of a second Portuguese lawyer, bringing their legal team to four.

Rogerio Alves is president of the Portuguese Bar Association and has worked on some of country's most high profile cases.

He will work alongside the couple's current Portuguese lawyer, Carlos Pinto de Abreu, whom the couple appointed a month ago when they were accused in the Portuguese media of being involved in Madeleine's disappearance.

It is thought that Mr Alves' fees will be paid out of the £100,000 that Sir Richard Branson has donated towards to the McCanns' legal fund.

Madeleine: Missing for 141 days

The new appointment means the McCanns have a fearsome legal team of lawyers working for them.

As well as the two Portuguese lawyers, they have also employed British solicitor Angus McBride and Michael Caplan QC, both of whom have formidable reputations.

Mr Caplan, in particular, is considered one of the country's foremost solicitors.

With his expertise and track record, he can charge upwards of £700 an hour for his services.

Yesterday all four lawyers had discussions with the McCanns at Mr Caplan's London office. The meeting lasted around around six hours.

Afterwards, the family spokesman Clarence Mitchell said: "It is effectively the doubling of defence skills. It helps to have extra firepower."

Detectives start again

In Portugal the authorities admitted yesterday for the first time that their case had stalled - and that they are prepared to re-explore the possibility that she was snatched by an abductor.

They made it clear that the McCanns are still prime suspects in the inquiry, but that the case had reached "an impasse" after 141 days.

The news brought quiet relief to the couple, who saw it as a significant turning point in the campaign to switch the focus back to finding their daughter.

From 1,000 miles away in the UK, they watched events unfold yesterday after Wednesday's dramatic announcement that there was not enough evidence yet to warrant charges or reinterrogation.

The back-to-basics turnaround in the investigation was revealed by the national daily newspaper Diario de Noticias, quoting sources close to Luis Bilro Verao, the senior public prosecutor brought in to lead the case last week.

It reported that Mr Verao said: "The investigation has now entered an impasse."

All possible theories - abduction, accident, murder or innocent disappearance - would be reinvestigated.

The newspaper further reported that the kidnap theory, virtually abandoned after detectives pinpointed the McCanns as suspects, was "still on the table".

Other sources confirmed that new searches would be carried out soon at specific locations, aimed at finding either Madeleine or any clue to what happened.

Spokesman: Clarence Mitchell said the appointment of a second Portuguese lawyer will be 'extra firepower'

While Mr Mitchell said the couple were relieved by the news that they would not face any immediate reinterrogation, he added: "There is still a long way to go in the legal process. They remain official suspects."

He said he could not discuss the DNA evidence at the centre of the police case, extracted from blood found in their holiday apartment and "bodily fluids" in the car they hired some 24 days after Madeleine disappeared.

But he added: "It's safe to say there are wholly innocent explanations for whatever the police may or may not have found in the car."

The McCanns, who could still be called back to Portugal if new evidence emerges, have also been offered help by a lawyer in Northern Ireland. Solicitor Paul Corrigan is defending an alleged Real IRA terrorist accused of murdering 29 people in the 1998 Omagh bombing.

The case has given him experience in challenging 'Low Copy Number DNA' or LCN DNA, a method of magnifying minute traces of body matter that are inadequate for more established DNA analysis.

Critics claims LCN DNA is not reliable enough to stand up in court - and it may be involved in the case against the McCanns.

And an intelligence expert has said photographs taken by spy satellites could hold the key to Madeleine's disappearance.

Professor Glees, who is director of Brunel University's Centre for Intelligence and Security Studies, said the little-known Joint Air Reconnaissance Intelligence Centre, based at RAF Brampton, Cambridgeshire, is a world leader in analysing aerial and satellite imagery.

It could collect and examine all the imagery that can be found of Praia da Luz, where the McCanns were on holiday, dating back to May 2. "It is perfectly possible that the European Commission's satellites, which track fishing boats, may also be able to shed light on Madeleine's fate. JARIC will quickly tell us," he said.