Britain has become the world's sixth largest importer of water - threatening world supplies, new figures have revealed.

Just 38 per cent of our consumption comes from domestic sources, with the rest  'virtually shipped in' from countries facing serious shortages.

The average person uses 4,645 litres of water every day.

Drinking and washing use up just 150 litres, then there are the 'hidden' gallons used in the production of our food and clothing.

Drying up: The WWF warns about the impact our food imports have on suppliers such as Spain, above

Reducing our consumption of this 'virtual water' is a major environmental necessity, according to research by the World Wildlife Fund.

The WWF report - the first attempt to quantify our water footprint and its impact - is being unveiled to a meeting of international experts in Stockholm this week.

It urges modern businesses to change production patterns which are leading to the slow death of vital streams and rivers.

Only Brazil, Mexico, Japan, China and Italy come higher in the league of importers of virtual water.

The charity's water expert Stuart Orr said: 'What's particularly worrying is that huge amounts of the water and cotton we consume are grown in drier areas of the world where water resources are either already stressed or very likely to become so in the near future.'

Water-starved countries which supply the UK with substantial imports include Spain, Egypt, Morocco, South Africa, Israel, Pakistan and Uzbekistan, which are all facing acute shortages.

Poorer countries typically subsist on just 1,000 litres of water per day - less than a quarter of the British average.

Much of this disparity is down to diet. A meat-and-dairy based diet consumes around 5,000 litres of virtual water per day, compared to just 2,000 litres for a vegetarian.

Experts say fresh water is being talked of as the 'new oil' at this week's World Water Forum in Sweden, as it is increasingly seen as a valuable and finite resource.

British retailers are already reportedly examining how much of their food comes from areas where water reserves are running out.

Marks & Spencer is working with WWF to calculate the water footprint of its entire food and clothing range, and may relocate key crops.

M&S's technical director David Gregory said the company had already started auditing the water footprint of five crops - strawberries, tomatoes, lettuce, potatoes and roses.

'We are already in discussion with WWF about out decisions about where to grow crops in the future,' he told the Guardian.

The report will put pressure on British supermarkets, which rely on southern Spain for salad crops such as lettuce, cucumbers, tomatoes and peppers throughout the winter.

Sainsbury's agronomist Debbie Winstanley said the supermarket was looking at security of supplies 10 years ahead, due to 'massive challenges' with crops based in places such as Murcia in southern Spain.

She said: 'From our point of view we've got to look at where our growers are going to get their water from.'