The Prince of Wales said the benefit to farmers would be enormous if organisations like the Army, hospitals and government departments spent their food budget on UK produce.

He dismissed the idea that such a policy would break EU rules, citing research recently completed at the University of Wales.

Charles said: "There are perfectly legal mechanisms to avoid this particular problem, which are often employed by many of our European partners who understand... the value of good quality, home-produced food."

'Just imagine'

It is thought that the NHS alone spends £500m a year on meals and could transform the fortunes of farmers single-handedly if it went along with the idea.

It is something which I think retailers need to consider as a matter of urgency Prince Charles

According to The Times Britain imports food and drink worth £18.5bn a year, compared to exports of just £8.5bn - figures which have incensed the prince.

Charles said in an interview with the magazine Farmers Weekly: "Our public bodies buy enormous quantities of food.

"Just imagine the amount of food purchased by our hospitals, armed forces, local government, schools and universities.

"What an impact it would make on the viability of the British farmer if each was to 'buy British' and preferably, buy 'local'."

'Sheer folly'

Turning to the idea that European legislation prevents the introduction of such a policy, Charles said there were ways around the problem.

He said that in parts of France and Italy, for example, schools were able to serve children locally produced food.

The UK is not self-sufficient in food production though, and may not be able to meet the demands created by a "buy British" policy.

Prince Charles said it was "sheer folly" for the UK not to be able to meet its own needs.

He said: "It is something which I think retailers need to consider as a matter of urgency.

"Continuity and accessibility of supply are of the utmost importance to them with the increased risk from terrorism and instability overseas."