Four major regions of the UK will be officially declared drought-stricken this week, in a move that is likely to see special powers introduced over water supplies on farms and businesses across large swaths of the country.

Wales, the south-west, the Midlands and East Anglia will be raised to official drought status, enabling the government and water companies to invoke extra controls over water supplies as a lack of rain afflicts a huge band across the middle of the country.

However, regions that have suffered drought in the past, such as Kent and the south-east, will be spared many of the restrictions as rainfall has been at normal or almost normal levels there in the past six months. Scotland and the north of England are also drought-free.

Paul Leinster, chief executive of the Environment Agency, said this year would not see a repeat of the scenes of 1976, as some commentators have predicted, as last winter there was enough rain and snowfall to fill reservoirs.

But he added: "It depends on what we see this winter – next year could be the crunch year."

The drought of 1976 followed a dry autumn and winter, during which stocks in reservoirs were severely depleted.

"We are in a much better position this year," he said. "Then, one of the big issues was that the previous year had been so dry, so you did not get a ground water recharge."

Leinster added that the UK's water supply system had been made more resilient in the intervening decades. "We have learned lessons since then," he said.

Although at present there are no domestic hosepipe bans in force in reaction to the drought, consumers may face restrictions if the dry weather continues.

Recent rainfall has not been enough to make up for the last six months, after the warmest spring since 1659 and the second driest since 1910. East Anglia was the worst afflicted region, receiving only a fifth of its average rainfall.

A map issue by the Department of Space and Climate Physics at UCL of the drought in UK over the last three months: from minor drought in yellow to exceptional drought in dark red. Photograph: Department of Space and Climate Physics/UCL

Businesses and farms in the worst hit areas are already suffering, as the Environment Agency has brought in changes to 70 licences to abstract water.

The agency is also looking closely at a further 200 licences to remove water from rivers and underground sources as the drought takes hold. Businesses affected are likely to include power generators, food processors, breweries and manufacturers, though the agency was unable to pinpoint specific companies.

One of the changes brought in that could become permanent is that farmers, especially in East Anglia, have been asked to irrigate their crops at night instead of during the day.

The Environment Agency said this made sense as irrigating fields in daytime leads to much of the water evaporating off, whereas at night the crops get the full benefit.

Farmers have resisted this change to their working practices as it is less convenient and they may have to rearrange staff working patterns. Most modern irrigation systems can be easily switched to different timings, however.

So far, farmers have made the move voluntarily, but Leinster did not rule out compulsion in future.

The Environment Agency is also helping to set up co-operatives to share water among farmers and other businesses that have licences to remove river water.

As oxygen levels in some rivers have fallen along with water levels, the agency has brought in special measures to save wildlife, including moving fish trapped in pools in the river Teme and river Lathkill, and putting in place pumping equipment to replenish oxygen levels, to protect fish and other aquatic life which could otherwise be in danger.

The agency said it was closely monitoring fish stocks such as migrating salmon and sea trout, both of which can be affected by low river flows.

Measures including water rationing in extreme conditions, could be brought in by ministers through drought order and drought permits if water companies demonstrate they need to conserve stocks and have followed all reasonable measures to avoid the restrictions.

Leinster said the key to protecting against future droughts was to use water more efficiently. This will mean preventing losses, for instance from leaking pipes, but could also mean greater use of metering in future.

But one of the problems with managing water use, he said, was the variation in rainfall across the UK. In regions where there has been a lot of rain, consumers are unsympathetic to concerns over shortages elsewhere, and unwilling to countenance water-saving measures.

"If you go to the north of England, to talk about the sustainable use of water, you would have a different conversation than if you went to Cambridgeshire," he said.

Leinster said the spread of drought this year showed the extent of annual variation in the UK.

"Kent and Sussex have both held up well in terms of rainfall, unusually," he said. "The pattern we are seeing this year is different to patterns seen in past years."

The variation showed how difficult it was to make plans for water provision in the decades ahead, when climate change is also expected to wreak further damage on water supplies – water flows in rivers in the south of England are predicted to be reduced by half or even 80% by 2050.

Flooding patterns remain equally unpredictable, with severe floods afflicting nearly all of the country's regions in the last decade, in both winter and summer.