The amount of water used to produce food is the biggest threat to Britain’s food chain, according to a leading scientist.

Professor Tim Lang, a senior government food advisor, said the way food is grown in the UK will have to change to counter the over-use of water in food production across the world.

Prof Lang, who devised the term ‘food miles’ more than ten years ago, said the water footprint of food was just as great as its carbon footprint.

People need to become more aware of how much water is used to produce staple goods, particularly meat and milk, he added.

“A major shift has got to happen and it has to be thought through very quickly,” he said.

“People can’t go on eating the same amount of meat and dairy produce they have been. It’s unsustainable.

“Animals consume a disproportionate amount of water to the amount of calories they provide. The current model of farming is going to have to change.”

According to the World Wide Fund, producing a pint of milk uses up over 550 litres of water, while a hamburger uses 1800 litres.

The figures take into account the amount of water used from the start to the end of the food chain, including irrigation of crops and processing.

Prof Lang, who is currently researching what constitutes a “sustainable” diet and has just published a book, Food Policy, on the subject, said he has urged retailers and DEFRA to begin water audits of food.

“The government is taking this seriously and will take action upon it.”