If you have ever seen Eddie Izzard perform his stand-up routine you’ll know how frantically, breathlessly exhilarating he is. No resistance is possible; he rewires your cerebral cortex with his surreal, madcap ramblings. It would be torture if it were not so funny.

Yet sitting down to chat to Izzard is, for the same reason, oddly unnerving. He is energetic and focused and funny, but I quickly sense that his mind is at its most dangerously adventurous when he is high-wiring an audience across boundaries of sense and good taste into his private realms of unmapped nonsense. Today, on the other hand, he seems hemmed in, a caged bird not singing.

Presumably it’s because we are having a serious talk about serious issues: the nasty things that dictators do to innocent people. Izzard is about to fly back to Britain to headline the Amnesty International revival of its famous Secret Policeman’s Ball at the Albert Hall in London. At John Cleese’s behest, Izzard had hosted Amnesty’s last big event, the 40th anniversary “We Know Where You Live” fundraiser at Wembley in 2001.

We are sitting under an umbrella in the hot sun at a West Hollywood cafe, but Izzard, 44, is looking incongruously New Bond Street in a crisp white open-necked shirt with blue cufflinks, which match his piercing blue eyes. He is sporting a goatee, which I hope he shaves off when he puts on his frilly dresses (Izzard is Britain’s most famous transvestite).

As we talk torture and imprisonment without trial and the horrors that man inflicts upon man, he does his best to make good sense of it all.

Yet, try as he might, Izzard, who turns out to be well read and knowledgeable about all sorts of macho things such as military history, cannot throw off the meandering, wildly discursive nature of his mind, so every now and then we tear away down strange tracks and blind alleys.

Look what happens when I ask him, as one of the headliners of The Secret Policeman’s Ball, whether he thinks humour can be an effective tool against dictatorship.

“If the humourless dictatorships are listening,” he says. “To some extent we are preaching to the converted. The people there say absolutely we shouldn’t have this, and the last time we had a dictatorship was whatsisface . . .”

“Cromwell?” I offer.

“Yes, Cromwell, and even he, apart from murdering the Irish, was generally trying to, I think, get power away from an idiotic king, Charles I, who thought he was appointed by God. But God never actually said that.

“People who talk to God always go off and do wars and things and kill people and oppress people. Can’t a liberal talk to God? He’d say, what you’re saying is a load of bullshit and when I talk to God he says, my idea is good and everyone should chill out, relax and all you dictators should go and drink hemlock.

“Hopefully the people who are in prison will hear that people are talking about them and that is great for them. The dictators? They definitely don’t want hassle; they just shouldn’t be there.

“That’s why I’m so passionate about Europe, because every colour of political s*** that could exist, we’ve had it. We’ve had the kings. We’ve had the dictators. We’ve had Vlad the Impaler, for God’s sake.