The gas meter reader was tracked down nearly five months after the murder on 26 April, a Scotland Yard spokesman said.

The inquiry team are trying to discover if the television presenter was the victim of an obsessive fan, or a contract killing.

They said they need to trace other men seen in the area in the minutes before the murder to find out how many people were involved.

The meter reader, who has not been named, confirmed to police that he had been in Gowan Avenue on the morning of the murder but felt he had no information to offer so did not come forward.

Police are still appealing for witnesses to come forward

The development was not viewed as a "great breakthrough" but cleared up the mystery of the man whose description did not match any others seen before the killing.

He had been spotted by a window cleaner who was working opposite Ms Dando's home, about 45 minutes before she was murdered on her doorstep.

Several sightings

The window cleaner saw a well-dressed man, whom he said looked like an estate agent, standing in the road talking on a mobile phone.

But this was just one of several sightings in the area before the killing and police still want anyone there that morning to come forward.

A man with black hair was seen by two neighbours leaving the scene of the murder just after 11.30am and there were at least five other sightings of unknown men in the 90 minutes before the murder.

There were further sightings of a man running down nearby Fulham Palace Road and a police e-fit was compiled of a man seen sweating heavily at a bus stop about 15 minutes after the murder.

Detective Chief Inspector Hamish Campbell, leading the investigation, said: "The witness was an important person to have traced.

"He had nothing to do with the murder but finding him is allowing us to establish whether one or more people were involved in the murder of Miss Dando.

"It is important for people to understand that it is vital that anyone in the area that morning must come forward so that we can eliminate potential suspects."