Norwich Union is one of the first insurers to set premiums based on a particular address rather than just a postcode band, for both residential and commercial properties. As well as showing whether a property is at risk, the map shows how often a flood is likely to occur and to what depth.

The multi-million pound project is initially launching in parts of Shropshire and Norfolk and will be rolled out across the UK, starting with high-risk flood areas. It is anticipated that the project will be completed by the end of 2004.

Shropshire has been selected as a key launch area following the devastating floods of October 2000 and ongoing flood risk. Norfolk was chosen because of the continued risk to properties on low-lying land.

And the insurer believes that more people are likely to benefit from the flood map because in some cases it may indicate that their property isn't in fact at risk or won't flood as often as previously thought.

Laurence Loughnane, head of underwriting at Norwich Union, says: "Although insurance companies can't stop properties being flooded, we believe we have a responsibility to ensure flood risk is calculated as accurately as possible."

Norwich Union worked with Intermap to collect data using an airborne radar system, to produce the 'Digital Elevation Model' - which shows the height of the ground above sea level. This was combined with a software model provided by JBA Consulting to produce the final map showing where floods are likely to occur, how they can spread and how far they can extend.

Rival insurer More Th>n says it already uses a 3D digital terrain model to accurately assess the risk of flood at an individual address.

Steve Kingshott, More Th>n home insurance manager, comments: "Whilst some insurers are reportedly introducing new flood risk mapping techniques,More Th>n has been using a sophisticated geographical risk analysis tool covering every property in the country for the last couple of years to ensure that all customers are treated fairly."