Ministers, farmers, supermarkets and utility companies will meet this week to assess the worsening dry spell gripping much of southern and eastern England and threatening to become an agricultural and environmental disaster.

Britain’s second-driest spring in 100 years and the warmest since records began in 1659 has left soil in parts of East Anglia and southeast England concrete-hard, with many rivers shrunk to trickles and crops withering at critical times in their growth.

Some eastern counties have had only 5mm of rain since the end of February, with most regions seeing no more than 60 per cent of average rainfall in the past four months, usually one of the wettest times of the year.

“The next few weeks are critical,” said National Farmers Union water adviser Jenny Bashford.

“If we get a heatwave now – and the forecast is for above-average temperatures and only sporadic showers in June – we are in a different situation.

“The north and northwest is largely okay but there are already significant problems in the south and east.”

The Government’s Environment Secretary, Caroline Spelman, asked the Environment Agency to report on how a full-scale drought might affect food production and prices, as well as water and power supplies.

Water companies, which have been upbeat so far about supplies, are likely to warn that some reservoirs in the south and east are beginning to empty.

Farming leaders warned Spelman last week that production across much of southern Britain was likely to be down by 15 per cent if normal rains resumed immediately and by much more if prolonged rains did not come soon. An increasing number of farmers predict yields will be reduced by 50 per cent or more.

George Dunn, a farmer near Winchester, Hampshire, said: “It’s too late now for many crops. Some farmers have destroyed their spring barley crop and replanted. We can expect the wheat harvest to be 10 per cent to 20 per cent down and the barley to be 30 per cent down. It will get very serious soon for livestock farmers.”