The satellite devices record precise property locations but do not take photographs

Postal workers in East Anglia are using satellite receivers to map the exact location of every property in a Royal Mail trial to improve sat-nav systems.

The devices record precise property co-ordinates in Essex, Cambridgeshire, Lincolnshire, Norfolk and Suffolk, but do not take photographs.

The initiative was in response to "market demand" for more accurate location information, a spokesman said.

He stressed postal delivery services would not be affected.

The distance-measuring devices will map the GPS longitude, latitude and altitude co-ordinates of every property in the trial area.

'Improve accuracy' Keith Jones, leading the "Pinpoint" project, said: "For individuals and companies, many everyday activities involve using information which is based on the location of an address.

"The emergency services, satellite navigation systems used by motorists and smartphone applications use this information.

"Mapping the co-ordinates which are accurate to the front door of addresses across the UK will help improve the accuracy of this information."

A spokesman for the Communication Workers Union said: "We raised concerns about resource and customer reaction to this new work and Royal Mail has taken these concerns on board.

"Postal workers who volunteer for this work in place of their deliveries will be fully trained."

The Royal Mail is sending a letter to every property in the trial area informing customers of the project and assuring them that no images or personal information will be collected.

The letter states: "With mail volumes in decline, it is important that Royal Mail continues to expand its range of trusted services.

"Royal Mail is undertaking this initiative in response to a need by businesses and consumers for more accurate local information."

If successful, the initiative will be rolled out across the UK later in the year.

BBC News Technology