What is it with the Prince of Wales? He seems physically incapable of keeping his mouth shut. Yesterday he was ranting about genetically modified crops, multinationals and climate change. But it might equally have been architecture, education or McDonald's, three of his previous obsessions. Next week it'll no doubt be the price of gas. And why haven't we heard his views on Georgia?

The Prince is as entitled to his views as anyone. What he is not entitled to do is share them with us. This has nothing to do with whatever merit they might or might not have. It has everything to do with the fact that one day he will be King.

Do you know what his mother thinks about GM crops? Do you know what the Queen thinks about anything? Of course not. Unlike her son, she realises that the moment she enters the world of politics - which her son did the moment that he started to lecture us about how the world should be run - is the moment that the monarchy ceases to exist. The monarchy is supposed to be a unifying force. The Prince's interventions serve only to divide.

Take his latest tirade. “Gigantic corporations” are conducting a “gigantic experiment, I think, with nature and the whole of humanity which has gone seriously wrong... Why else are we facing all these challenges, climate change and everything?... I think it's heading for real disaster.”

The attacks on further GM experiments - which, by definition, are designed to further our knowledge - expose the ignorance behind Prince Charles's remarks. There is not a shred of evidence - not a jot, not a hint, not a fraction - that there is any risk from GM crops. Even the European Commission, which operates on the precautionary principle, can find none. In 2001, it published a summary of 81 scientific studies conducted over 15 years. None found any evidence of harm to humans or the environment. The same conclusion has been reached by every academy of science that has examined the issue, in France, the US, India, China, Mexico and Brazil. Our own Royal Society has published four different reports.

I've yet to hear Prince Charles decry the use of insulin for diabetics as a “real disaster”. But if he rejects, on principle, the idea of GM crops, he should, because the insulin used is genetically engineered - the human gene that codes for insulin has been transferred into bacteria and yeast, a process that involves crossing the species barrier.

But then ignorance need not be consistent and when the Prince opens his mouth he serves only to advance the cause of an unthinking, irrational, ignorance as a basis for policy.

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