The McCanns have been left to co-ordinate their own inquiry after the Portuguese police investigation, widely regarded as deeply flawed, was closed.

Events in Praia da Luz on the evening of May 3 2007 have been scrutinised by police, private detectives and the media across the globe.Mr Williams-Thomas criticised several aspects of the Portuguese investigation, including botched searches and a complete failure to secure the crime scene.

He said the reliance on evidence of dogs trained to detect dead bodies was "significant and damaging", leading police to mistakenly focus on the McCanns.

Mr Williams-Thomas said the couple were made suspects, or arguidos, as a result of ambiguous evidence from specially-trained British dogs and their handlers.

And he said Portuguese author- ities must also act to register known paedophiles to stop the country becoming a favoured destination for criminals.

Mr Williams-Thomas said: "It is now clear that, after the Portuguese police failed to establish or identify any possible suspects during their initial investigation, and when they came under increasing pressure to resolve the case, they turned their attention on to Madeleine’s parents.

"In particular, they over-relied on the evidence of the dog team – such as it was, and it was this that prompted them to make Gerry and Kate McCann arguidos.

"In short, they concentrated on their theory that Madeleine had been accidentally killed and that her parents had later hidden her body.

"Although how they would have been able to have done this does not seem to have been considered by the Policia Judiciara."