By JAMES TOZER

Last updated at 01:47 07 December 2007

A colleague of John Darwin's wife tipped off police that he may still have been alive after overhearing her having whispered telephone conversations at work, it emerged yesterday.

The employee at the doctors' surgery where Anne Darwin worked as a receptionist apparently became suspicious after hearing snatches of calls made in the run-up to her sudden move to Panama.

The workmate, believed to be another woman, is thought to have already harboured doubts about whether Mr Darwin had really drowned while canoeing in the sea, as the inquest had concluded.

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She deduced from Mrs Darwin's manner that she was talking to her supposedly dead husband and informed police, who reopened the investigation into his death.

The revelation suggests the couple were secretly planning her decision to sell up and move to Central America.

The work colleague is expected to give a statement to detectives investigating the suspected fraud.

Mrs Darwin had been working as a receptionist at a doctors' surgery in County Durham at the time of her husband's disappearance.

This week she told the Daily Mail that her colleagues had been extremely supportive following his supposed drowning and that she returned to work about three months later.

But yesterday it emerged that it was hushed calls Mrs Darwin had made and received, apparently while working at Gilesgate Medical Centre over the summer, that put police on her husband's trail again.

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A source said: "The amount of calls Mrs Darwin was getting on her phone didn't raise any suspicions at first, but while the conversations she was having were always private, some of them were overheard.

"The tone of the conversations led the person that contacted the police to believe she was talking to the man who was supposedly dead, and the investigations basically started again from that point."

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The "careless whispers" suggestion was taken seriously by Cleveland Police, which had also looked into a reported sighting of Mr Darwin outside his former home two years earlier.

Mrs Darwin is understood to have told officers on that occasion that the man was a cousin who simply looked like her husband.

The doctors' surgery tip-off coincided with information that her son Mark had wired the proceeds of the £160,000 sale of another of their properties in March to her bank account in Panama.

Detective Superintendent Tony Hutchinson said: "There was some information which was reported to us three months ago to suggest that perhaps there was something suspicious with regards to his disappearance."

However he stressed that there had been no concrete evidence that Mr Darwin was indeed still alive until he reappeared in London at the weekend, saying he had been as surprised as everybody else. The staff member who sparked the investigation could not be contacted yesterday.

Practice manager Dave Harris confirmed Mrs Darwin had worked there, adding: "She is a former member of staff but I don't really want to comment on it, as it is a police matter."