THE number of properties blacklisted by insurers is set to double to 1m as the government releases its first maps of urban areas with inadequate drainage.

At present, half a million homeowners live in areas classified as “high risk” by the Environment Agency (EA) and are penalised with a supplement of up to 30% to their premiums and excesses of as much as £30,000.

Phil Rothwell, head of flood risk management at the EA, said that it had been forced to act by last year’s floods which caused havoc in Hull, Leeds and Birmingham.

He said: “We’re hoping to put in place new mapping systems very shortly to try to understand and define where pluvial flooding [where drains are unable to cope with flash floods] may be a problem.”

The agency has been forced to act because of pressure from the insurance industry, which made payouts of almost £3 billion for last year’s floods. It blames the government for a £150m shortfall in spending on flood defences.

The potential threat to 1m homes has been revealed by JBA Consulting, which has worked with the Department for Environment, Food and Rural Affairs and Norwich Union, the insurance company.

It is understood that JBA is advising the EA, in line with recommendations made by the Pitt Review, the official inquiry into last year’s floods. It has already drawn up flooding models in parts of London, Hull, Birmingham and Leeds.

An area is designated as high risk if there is a 1 in 75 chance or greater of flood damage in a given year. Although the EA’s designation is not binding on insurers, it is used by the industry as the basis from which to calculate flood risk.

At present, homeowners living in a high risk area are given some measure of protection under a 2002 agreement between the insurers’ trade body, the Association of British Insurers (ABI), and the government.

Homeowners can normally rely on cover if they stay with their existing insurer, but they face inflated premiums and high excesses. However, this deal is now at risk, with the ABI warning that its members will honour it only if it is convinced that the government is keeping its side of the bargain by investing enough in flood defences and drainage.

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