Police are trawling through Kate McCann's confidential medical records amid suspicions in Portugal she may have a history of depression, sources close to the investigation revealed today.

The detailed analysis of her medical notes could provide them with significant evidence against the doctor, now being treated as a suspect in the disappearance of her daughter Madeleine.

News of the development comes as a judge blocked a request from the Portuguese police to re-interview the McCanns in Portugal. Judge Pedro Daniel Dos Anjos Frios said they could be questioned by British authorities in the UK.

The re-interviewing will only take place when further DNA testing in Birmingham is completed, either tomorrow or Wednesday.

British officers are also looking through Madeleine's medical records to see whether or not the missing four-year-old could have suffered an allergic reaction to sedatives.

Since Kate and Gerry McCann were named as official suspects last week, there have been suggestions in Portugal that Madeleine was given drugs on the night of her disappearance.

The accusations have been strenuously denied by the couple but have not been ruled out by police. Although the order to seize medical files came from the Portuguese authorities, the background searches are being carried out by Leicestershire police.

A copy of Mrs McCann's diary has also been seized by police, who are now waiting for permission from the judge to seize and dismantle the McCanns' hire car so they can search for "traces of skin".

It has been reported that DNA evidence with a match to Madeleine was found in the Renault Scenic 25 days after their daughter vanished.

Yesterday it emerged the McCanns are trying to knock down potential evidence retrieved after two British sniffer dogs, capable of detecting blood and human remains, were used in the investigation in August.

One of the dogs picked up a "scent of deathî on items ranging from Mrs McCann's clothes to Madeleine's favourite soft toy Cuddle Cat.

Leaked reports from the investigation have suggested that Madeleine's parents could have accidentally killed her and then disposed of her body using the car. Although they do not know the full details of the Portuguese prosecutors' case against them, the McCanns are concerned that it may rest on the dog's reaction.

The couple's legal team has now consulted the lawyers of an American man accused of murdering his estranged wife in a case where "cadaver dogî evidence was central. They want to highlight the judge's dismissal of such evidence in the high-profile Eugene Zapata murder trial in Madison, Wisconsin.

Mr Zapata's estranged wife, flight instructor Jeanette Zapata, was 37 when she vanished in October 1976 after seeing her three children off to school. Her body has never been found. Detectives suspected Mr Zapata of involvement in her disappearance but did not charge him because of a lack of evidence.

Police decided to conduct new searches using cadaver dogs and Mr Zapata, 68, was charged with firstdegree murder last year after the dogs indicated that they had scented human remains in an underfloor crawl space at the former family home and other properties linked to him.
But the judge ruled that the dogs' ability to detect remains was too unreliable, noting that no remains had actually been found.