In my book on conspiracy theories, Voodoo Histories, first published in 2009, I devoted two pages to the phenomenon of Dieudonné M’bala M’bala. I saw him as an exemplar of an unofficial alliance between the far left and the far right, which combined an anti-imperialism (in reality an anti-Americanism) with an antisemitism masquerading as anti-Zionism.

Since then Dieudonnism has entered Britain in the shape of the footballer Nicolas Anelka (right) and his performance of the quenelle salute.

Dieudonné did not himself need to set foot in this country for his ideas to reach these shores. The world simply doesn’t work like that any more. Anyone who wants to can discover what he says or watch his videotaped performances on the internet.

Many of the people — mostly young men — who gravitate towards his form of anti-establishment populism, are precisely those most likely to access him in this way.

More, it is an essential part of their and his world-view that they are somehow oppressed and silenced by a system — partly run by the Jews (sorry, Zionists). In their own eyes, they are the put-upon, the oppressed, the shunned, the ones with a grievance.

I am, in any case, opposed in almost all situations to banning speech, unless it constitutes incitement to hatred and violence. We all of us depend on the right to freedom of expression, even if people dislike what we say.

Though, of course, should someone enter this country and break our laws, then I think we are entitled to act.

But pre-emptively banning a performer, a provacateur, like Dieudonné from entering Britain merely enhances the beliefs of his supporters and strengthens his status as a dangerous rebel.

And it does so without any concomitant gain in terms of restricting the spread of his ideas.