Madeleine: The McCanns are victims of a 'witch-hunt', says Britain's former top police officer

Lord Stevens said the 'sheer inadequacy' of the Portuguese inquiry would make it 'an outrageous miscarriage of justice' for Kate and Gerry McCann to face charges over their daughter's disappearance on May 3.

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"There's absolutely no chance they would be charged with murder in this country," he said.

"I've been a detective at the most senior level for 30 years and have never seen such a witchhunt, or one based on such flimsy evidence."

In the most damning indictment of Portuguese police so far, Lord Stevens said there was 'not a single shred of evidence' against the McCanns.

They did not fit the profile of parents who would kill their child, he said, and it was most likely that four-yearold Madeleine had been abducted.

Lord Stevens' attack on the Portuguese inquiry came amid reports that crucial evidence inside Kate and Gerry McCann's holiday apartment was contaminated by ash from policemen's cigarettes.

The ash was found among forensic samples, the Sunday Mirror reported.

New officers drafted in to help the investigation were horrified by the discovery.

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The original team ignored key leads and left vital information lying around so chaotically that new officers had to spend more than two weeks putting it all on computers, it was claimed.

Lord Stevens, who led a massive inquiry into the death of Princess Diana after retiring from Scotland Yard in 2005, said: "The police investigation that started so disastrously has turned to farce.

"Every apparent stream of evidence has been either missed or fatally compromised or is simply ludicrous."

The McCanns have had to endure claims that they accidentally killed their daughter, then hid her body and staged an abduction, accusations they vehemently deny.

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Portugal's most senior detective appeared to admit yesterday that mistakes had been made.

Alipio Ribeiro, national director of the Policia Judiciaria, said: "We have to give a new thrust to the investigation and try to understand signs that perhaps we didn't in the beginning".

Gerry McCann has begun talks with medical chiefs at Leicester's Glenfield Hospital about returning to his £75,000-a-year post as a consultant cardiologist, his spokesman said yesterday. He hopes to be back by Christmas.

His wife, a GP, has always ruled out working again while Madeleine is missing.