Something quite remarkable has happened. A group of adults, apparently of sound mind, has told George Clooney that it does not want to see – or hear – from him. That group was nothing less than the United Nations.

Clooney is the latest of the UN's showbusiness 'ambassadors' and, in that capacity, had recently travelled to Darfur, witnessing at first-hand the conditions which – according to many observers – make some sort of UN peacekeeping force essential.

We are told that this was the message which the great actor was going to give to the UN's delegates in New York. Certainly the press had descended en masse to hear Clooney lecture what is invariably called "the international community" on its duty; but then, just as the lights were about to go on, instead of saying 'Action!' – someone pulled the plug.

More precisely, a group of national delegates – widely suspected to be led by Russia and France – declared that they had no wish to be lectured on their political responsibilities by some American actor. Or, as the Russian spokeswoman put it: "this is not an appropriate forum for Mr Clooney to attend". Maria Zakharova added – perhaps just in case anyone should think her country was declaring war on Hollywood: "Russia is fully supportive of the actions of celebrities in stressing the UN's role". Angelina Jolie will doubtless be greatly relieved to hear that, not to mention Geri Halliwell.

Now we all know that Russia – and indeed France – conducts its foreign policy with a studied and remorseless cynicism. We also know that the UN has – despite half a dozen resolutions – not exactly distinguished itself in its dealings with Sudan. I suppose we should all be very angry that George Clooney was prevented from lecturing the General Assembly.

Yet my immediate reaction on hearing of this snub was to give a little cheer. At last a group of people have turned around and said to one of the growing band of actors, rock stars and models who think the world must listen to their profound thoughts (on everything from climate change to nuclear proliferation): we really don't need to hear from you. Clooney might be right and the Russians might be wrong, but something rare and wonderful has happened when showbusiness is put in its place (which is not necessarily the General Assembly of the United Nations).

Perhaps such a rebuff could only have happened at the hands of an emissary of Mr Putin's government, with its bullish – not to say thuggish – contempt for everything the West holds dear (and nothing is held more dear than the movie business). It's certainly hard to imagine any British or American politician treating showbiz royalty with such lack of consideration.

In this country Gordon Brown and David Cameron frantically compete for the sympathy and endorsement of those we term "celebrities". Bob Geldof – who is, admittedly, a substantial figure outside the recording studio – must have lost count of the times he has been begged to join one or other of our main political parties. Come to think of it, it seems most unlikely that either the Liberal Democrats or UKIP would have failed to ask for his blessing, too.

In America there is a completely incestuous relationship between Hollywood and politics. For example, the stars of The West Wing are now regularly asked, by apparently serious newspapers, to give their views on the various "real" Presidential candidates. I suppose there is nothing at all new in this. For almost 40 years the president of the Motion Picture Association of America – in other words "Mr Hollywood" – was Jack Valenti. Before arriving in Hollywood Mr Valenti had been fixer-in-chief for the Democrat President Lyndon Johnson. There is some evidence to suggest that, invaluable as Johnson found Valenti in the White House, he was even more useful on Sunset Boulevard.

Los Angeles, like California as a whole, is traditionally seen as fertile territory for the Democrats, so the scramble by Hillary Clinton and Barack Obama for the endorsements from Hollywood have taken on a peculiar intensity and ferocity. In a way, they are absolutely right to care so much. Film stars are trusted in a way that no politicians are – or indeed no other group in society. Why they are thought to be such paragons is a mystery to me. Such evidence as we have suggests that most of Hollywood's greatest names are (and always have been) either crazed or on drugs – and probably both.

Naturally, we must exclude the ineffably clean-cut George Clooney from these strictures. Mr Clooney makes a great deal of money appearing in advertisements for Martini and Budweiser, but these are legal substances without which the American economy could very easily grind to a halt. It is obviously a public duty to promote these brands and it in no way detracts from Mr Clooney's very obvious sincerity as a man interested only in his art and the truth.

Jack Valenti always argued that there was nothing strange in the marriage of politics and showbusiness: he was fond of saying that "Politicians and movie stars spring from the same DNA". He had a point. Actors, if they are any good, have a gift for making an audience believe whatever they want them to believe. The greatest actors also have the ability to draw on the emotions of the audience to create an extraordinary bond of intimacy. There can be few politicians who do not covet those skills – and a very few, such as Tony Blair, who actually possess them in some small way.

There was, of course, the extraordinary instance of Ronald Reagan, the most vivid and triumphant example of Jack Valenti's dictum. Reagan, particularly in this country, is frequently mocked as an illustration of the embarrassing consequences of actors meddling in politics: it is said that he was just an empty vessel who would simply emote whatever lines he was given to say, without really understanding the true significance of any of it.

Actually Reagan was a much greater politician than he was an actor; and far from being a tabula rasa awaiting the imprint of others' ideas, he was a man of the most rigid principles. He didn't just act the part of a person with passionately-held views. Those really were his opinions. So when he referred to the Soviet Union as "an evil empire" he shocked some of his political advisors, who rather wished he could have been a little less sincere.

Perhaps George Clooney – despite his evident distaste for everything that Ronald Reagan stood for – might have emulated the tone of the Fortieth President, when dealing with the Russians' attack on him last week, instead of just joking that "I think I've lost my touch". Whatever else, it would have been a wonderful piece of theatre.

d.lawson@independent.co.uk