As many as 4.3 million people in England and Wales are at risk of dams failing and bringing deluges of water travelling up to 18 miles (30km) downstream, a report cautioned yesterday.

Those under threat include children and students at about 800 schools or colleges, and police, fire and ambulance staff based in 400 emergency centres.

Few are aware of the risk and, in a radical move, ministers have now been told to scrap secrecy rules and give people the right to know if their lives or homes could be endangered by the network of 2,000 large dams and reservoirs. Of these, 956 are categorised as posing a risk to life if they breach.

France and the United States already operate an open policy on flood risk. In Britain the Centre for Protection of National Infrastructure, an arm of MI5, classifies the information as a state secret because of a possible risk of terrorist attack.

Times Archive 1953: National action for flood relief

Mr Churchill said all the resources of the country were mobilized to rescue and succour victims

• 1968: Good neighbours ease the burden in flood areas

• 1970: Danger of Humberside flooding

The need to keep local communities informed of the scale of the threat from flooding emerged as a key recommendation from the review of last summer's severe flooding by Sir Michael Pitt, who called for the publication of every map that shows the potential route of flooding from a dam.

There is particular concern about the number of large reservoirs sited near built-up areas. The Ladywell reservoir, for example, is considered a threat to Birmingham.

Others close to populated areas are the Rivington chain of reservoirs in the west Pennines, north-west of Manchester, and a cluster of reservoirs on Exmoor. The threat from some 3,000 small raised reservoirs should also be assessed and disclosed, the Pitt report recommends.

A full response from the Government is expected this autumn but an immediate £1 million to improve mapping of reservoir safety was pledged by Hilary Benn, the Environment Secretary.

The need for wider dissemination of the threat was reinforced by the near failure of the Ulley dam, near Rotherham, last year. Emergency services had no clue which areas were at risk and officials had to work on Ordnance Survey maps through the night to calculate worst-case scenarios.

About 1,000 people were evacuated and a section of the M1 closed after a 20-metre gash appeared in the Victorian dam, which holds back 100 million gallons of water.

The Pitt review considered this incident an unnecessary risk and said that contingency plans for a breach should have been ready in advance.

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