McCanns: We can prove that we didn't sedate our children

Results of tests carried out on their two-year-old twins, Sean and Amelie, are understood to show the children have never been given sedatives, according to the Daily Mail's sister paper, the Evening Standard.

The tests are expected to form a crucial part of the McCanns' legal defence against Portuguese police claims they are implicated in the death of their four-year-old daughter Madeleine, who vanished almost six months ago.

The allegation that the McCanns regularly drugged their children to make sure they went to sleep on time is key to the police case against them.

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The Policia Judiciaria have suggested Madeleine died as the result of an accidental drugs overdose and that the McCanns, both doctors, covered up the death to protect their careers.

But a source close to the McCanns said they have now gathered irrefutable proof the children were never drugged.

The Standard understands samples of hair were given to a forensic team hired by the McCanns' lawyers for analysis. The toxicology tests performed on their hair are understood to show no traces of sedatives. The test results are part of a dossier of evidence compiled by the McCanns' legal team at law firm Kingsley Napley, to show they were not involved in their daughter's disappearance from their Algarve holiday apartment on 3 May.

As well as dismissing the drug theory, the lawyers have evidence to disprove allegations that Mr McCann is not the biological father of Madeleine, a claim which is significant because the McCanns are arguing that DNA evidence in the boot of their hire car comes from the twins rather than the missing child.

A source close to the couple said: "It would be logical for tests to be carried out on the twins to show they have never been given sedatives. It would be right to say those tests show no evidence of sedatives in their systems. It backs up Kate and Gerry's claims they have never sedated the children and explains why they are so certain they can prove the allegation is just another police smear."

The McCanns have threatened legal action against 24 Horas, a Portuguese newspaper which, citing police sources, has repeatedly claimed the children were sedated on the night Madeleine vanished. The results of the tests will also form a key element in any future libel proceedings, which could take place in a British court - where damages can be punitive - because 24 Horas publishes on the internet.

The McCanns were made official suspects following the analysis of forensic evidence gathered from inside the family's apartment in Praia da Luz and also from a hire car, rented 25 days after Madeleine vanished. Further test results carried out at the Forensic Science Service laboratory in Birmingham are due back in Portugal as soon as today.

These could be critical in determining whether the McCanns, back at home in Rothley, Leicestershire, are charged in connection with their daughter's disappearance or formally cleared of any involvement.