Farmers in the Fens are being told to water their crops by night, as the Environment Agency draws up emergency plans to tackle a summer drought.

Ministers, farmers and utility companies are meeting this week to discuss the growing crisis.

Environment secretary Caroline Spelman has asked the Environment Agency (EA) to prepare a report on the impacts of the drought.

East Anglia was the driest part of the country in May, the EA's chief drought officer said last night.

While most of southern England received between 58pc and 64pc of its expected average rainfall last month, the East saw just 47pc – less than 5mm of rain since February in some areas.

Farmers' leaders fear a prolonged dry spell will reduce crop yields and push up food prices.

Soils are said to be the driest they have been for 50 years. Growers in the Fens, between Cambridge and King's Lynn, are being asked to water their crops at night.

Those who abstract water from rivers and boreholes are licensed by the Environment Agency, which limits the amount they can take to irrigate their fields.

Stuart Sampson, the EA's national drought co-ordinator, said the agency had asked 140 licence holders for 'voluntary restrictions' to safeguard supplies. 'Farmers are irrigating during the night to reduce water lost to evaporation following agreement between us, farmers and other abstractors,' he said.

'Some water abstraction licence holders across parts of England and Wales have had to stop abstracting due to conditions on their licence which are linked to low river flows.'

Mr Sampson said continued dry weather would increase the pressure on supplies as the drought impacts on the environment.

'We would expect to start seeing more environmental impacts such as dried-out ponds, fish struggling for oxygen and algal blooms,' he said.

'These impacts tend to occur in the height of summer, in response to heat waves and when absolute flows are at their lowest.'

So far, Anglian Water has said it does not expect to have to impose hosepipe bans. But water companies in the West Country are urging gardeners to go easy.

Rivers in the South-west and Wales are suffering from low flows. EA scientists fear low water levels could harm salmon and sea trout populations, by preventing the fish from reaching their spawning grounds.

Mr Sampson said the EA would publish a report predicting the impacts of the drought and plans to manage it by the middle of this month.