He has championed youth achievement and the conservation of wildlife. Now the Duke of Edinburgh has turned his thoughts to solving the global food crisis.

Prince Philip emerges in a television interview this week as the model royal “eco-warrior” who believes overpopulation has contributed to the pressures on the world and that anyone who believes in God should go green.

The duke hints that curbing family sizes may be the best means of keeping the soaring cost of staple food products, such as bread and rice, in check.

“Food prices are going up,” he tells his interviewer, Sir Trevor McDonald. “Everyone thinks it’s to do with not enough food, but it’s really that demand is too great – too many people. Basically, it’s a little embarrassing for everybody. No one quite knows how to handle it. Nobody wants their family life to be interfered with by the government.”

Whether Philip, who has four children with the Queen and eight grandchildren, is contemplating a Chinese-style one-child policy for Britain or other, more radical ideas, remains unknown.

McDonald, who interviewed the duke for a two-part television documentary, has pointed out: “If he launches into a flow, it is not proper to interrupt.”

However, some of the duke’s previous observations have landed him in hot water. During a royal tour of China in 1986, he managed to insult his hosts by telling a group of British students not to stay in the country for too long in case they developed “slitty eyes”.

His latest comments will be broadcast tomorrow and on Tuesday on ITV1. The documentary shows that Philip, 86, became involved in green initiatives long before his eldest son. He explains how he enlisted religious leaders, including Pope John Paul II, to the environmental cause. “It seemed to me that most religions attributed the world to some special creation and I said, ‘Well, look, if you believe God created the world, you ought to take an interest in its wellbeing’.”

The duke’s eco-credentials go back to the 1970s when he fitted solar panels to a private cottage on the Sandringham estate. Although he was well ahead of the times, he confesses that the panels saved him only about 10% on fuel bills.

Despite taking the newscaster on a tour of the Sandringham estate in a gas-guzzling Land Rover, the duke uses a black cab run on liquefied petroleum gas to get around London.

The use of such transport can have unintended consequences. Hugo Vickers, a royal historian, said: “On at least one occasion someone has seen a taxi, gone up and tapped on the window and asked the so-called taxi driver the way to somewhere else, and has been seen wandering off scratching his head and wondering if he really has just seen the Duke of Edinburgh.”

Philip, international president emeritus of the World Wide Fund for Nature, has been passionate about conservation work for many years. He is at pains, however, to point out the difference between conserving species and the “huge emphasis” placed on animal welfare today.

The distinction provides him with a defence for more bloody country pursuits, such as pheasant shooting and fox hunting. “People don’t realise it is the species that matter – not the individual – from the conservation point of view,” he says.

“You’ve got to be fairly hard-hearted about it. Conservation is not a romantic business. It’s a very practical business, trying to ensure as many different species of wildlife can exist, and which means in some cases controlling some so the others can have a better chance.”

The ITV documentary has been cleared by Buckingham Palace and the first part will be screened on the same day that Peter Fincham arrives at the broadcaster as its new director of television.

Fincham resigned as controller of BBC1 last year after wrongly edited footage of the Queen was used in a trailer. The film was edited to make it appear as if the monarch had stormed out of a shoot with Annie Leibovitz, the photographer.

The row over audience deception reappeared last week as ITV was fined a record £5.7m by Ofcom, the media regulator, for rigging competitions on a series of shows, while the BBC admitted that it had kept more than £100,000 from phone-ins that should have gone to charity.

Last night Don Foster, the Liberal Democrat culture spokesman, called on the Serious Fraud Office and the police to investigate the scandals.

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