Russell Brand has laid into Prime Minister Tony Abbott, labelling him a 'raving lunatic' - weeks after he hinted he was sympathetic to 9/11 conspiracy theories and joined throngs of masked anti-capitalist protesters at a rally in London.

The comedian's remarks were broadcast in a promotional interview for his new book, Revolution, an anti-capitalist manifesto which shares themes with a recent 'anti-corruption, anti-democracy' protest Brand attended and then ditched for a glitzy theatre gig last month.

In the Nine News interview, Brand dubbed Mr Abbott 'one of the worst' world leaders.

'Have a look at him... I am pretty sure he is an absolute raving lunatic and the people across Australia are unhappy,' he said.

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Taking aim: Russell Brand (pictured right) has branded Prime Minister Tony Abbott (left) an 'absolute raving lunatic'

'Have a look at him,' Brand said, 'I'm pretty sure he's a stark raving lunatic'

Brand needed to be reminded about who the nation's leader was before he launched into his spray at Tony Abbott

But his opinions about the nation's leader could not be that strong.

Brand needed the reporter to remind him who the prime minister was.

'Who's your one who's in charge of you now?' he said, before launching into his spiel.

In the new book, Revolution, Brand questions whether capitalism is the best system for the world. Those were themes shared by the recent protest he attended, the Million Mask March, earlier this month.

But Brand copped considerable flak in the British press and on social media after it was revealed he rushed off from the march to attend the important theatre gig.

Sophie Lak wrote: 'Russell Brand loves a revolution but then leaves demonstration early to go to a celeb freebie party #fakeass'

Terence McLeod ‏tweeted: 'Russell Brand worth £12 million, joined an attack the rich protest last night. Oh the irony!'

In an interview with the BBC, Brand said: 'I went along before visiting the opening night of Made In Dagenham, my family are from Dagenham.

'I was in the difficult position of being at an anti-corruption, anti-democracy protest and then saying "my god, I've got to rush", I've got to be at the theatre.'

He said he got to the musical 'during the opening number' but insisted he had acted like a 'substitute teacher' at the demonstrations by telling protesters to 'calm down'.

The Brand manifesto? The comedian questions the foundations for global capitalism in his new book

In October, Brand told the BBC's Newsnight program that people should be 'open-minded' about the idea the U.S. government was behind the 9/11 terrorist attacks.

'I think it is interesting at this time when we have so little trust in our political figures, where ordinary people have so little trust in their media, we have to remain open-minded to any kind of possibility,' he said.

'Do you trust the American government? Do you trust the British government?

'What I do think is interesting is the relationship that the Bush family have had for a long time with the Bin Laden family.'

The comedian was also the subject of a light-hearted pasting recently after a Twitter user observed that Brand's new manifesto read like lyrics from the famously nonsensical Blur song, Parklife.

'Russell Brand's writing feels like someone is about to shout 'PARKLIFE" at the end of every sentence,' Dan Barker wrote, in a reference to the 1994 hit.

For a period afterwards, every time Brand tweeted afterwards he was deluged with tweets saying: 'Parklife!'

In response, Brand shot his own politically themed Parklife parody video.