The good news: it's hotter than North Africa. The bad news: there's now a hosepipe ban

Large parts of Britain are set for a week of warm weather that will see temperatures equal those in parts of North Africa, forecasters have predicted. But water companies said a worsening drought trailing in its wake would see hosepipe and garden-sprinkler bans introduced shortly across southern and eastern England.

Days after an advertising campaign starring Stephen Fry, Julie Walters and Rupert Grint was launched to convince more British people to holiday at home, Met Office forecasters predicted sunshine for most of the country. London and eastern Britain could see temperatures rise to 18C and higher, they said. A Met Office spokesman said: "Britain will have a warm week with around 15C on average, rising to a peak around Thursday when they will reach around 18C or possibly slightly higher in parts of the South East of England."

He said temperatures were likely to reach the same level as those in Tunis on Thursday, although western England was more likely to see cloud with chances of showers and lower temperatures.

The Centre for Ecology and Hydrology said rainfall over lowland areas of England in had reached its lowest point since 1963 in January and February. Restrictions on water use are to be brought in by seven water companies in the face of the increasingly severe water shortages brought about by two successive, very dry winters.

The cutbacks will be led by Thames Water, which will impose a hosepipe ban on all its 8.8 million water customers in London and the Thames Valley from 5 April, at the start of the Easter bank holiday weekend.

It will be joined in restrictions by Southern Water, South East Water, Thames Water, Anglian Water, Sutton and East Surrey, Veolia Central and Veolia South East are all bringing in restrictions on water use in the drought-stricken South East and East Anglia regions. Thames Water acknowledged that the move would not be popular but said it would conserve water and put the needs of families first. It said groundwater levels in the region were close to the lowest ever recorded and many tributaries of the River Thames are running very low, particularly the River Pang, which is running at a third of average flows in Berkshire.

The river, home to Wind In The Willows' Ratty, has dried up entirely upstream of Bucklebury for seven miles north to its source at Compton. The Thames Water chief executive Martin Baggs said the company had done as much as it could to save water, for example by reducing leaks, but groundwater levels were well below where they should be after two dry winters.

"We know these restrictions will be unpopular, but they will save a lot of water. A garden sprinkler uses as much water in an hour as a family of four uses in a day and when water is in short supply, the needs of families must come first," he said.

The temporary-use ban forbids hosepipes for gardening, recreational uses such as filling swimming pools or paddling pools and for cleaning, except for specific exemptions. Thames Water said it would prosecute breaches of the ban if necessary, but hoped customers would help it save water.

Mr Baggs said: "If the dry weather continues, none of us can rule out the possibility of applying for a drought order from Defra, which would result in extended water-use restrictions."

British weather: three-day forecast

Tuesday will have a chilly start that will give way to a dry afternoon with warm sunshine in most parts of the country. The night will remain dry for most of the UK with clear spells, but forecasters predict it will become chilly.

Wednesday will be dry in most of the UK with any fog and low cloud that has settled slowly lifting to leave sunny spells during the afternoon.

Thursday is set to see a foggy start. Most of the country will be dry and sunny but it will be cloudy at times in the North and west, with the chance of patchy rain across Scotland during the afternoon.