A book by alt-right leader Milo Yiannopoulos has been cancelled just hours after he was uninvited as a speaker at one of America’s most significant conservative conferences.

It follows the resurfacing of a video which showed him speaking positively about sexual relationships between boys and men.

The senior editor at conservative news website Breitbart is no stranger to controversy — his now-cancelled book was called Dangerous, and he’s made a career out of attacking feminism, political correctness and Islam.

But comments he made during a conversation with the Drunken Peasants podcast early last year were the final straw for the Conservative Political Action Conference (CPAC) which is being held in Maryland this week.

During a discussion about consent, Mr Yiannopoulos referred to “coming of age” relationships which occur “in the homosexual world, particularly”.

“Those older men help those young boys to discover who they are and give them security and safety and provide them with love,” he said.

Mr Yiannopoulos specifically referred to relationships between 13-year-old boys and older men.

He also referred to abuse he himself experienced when he was a child, saying, “I’m grateful for Father Michael. I wouldn’t give nearly such good head if it wasn’t for him.”

As you can imagine, there was a big reaction when videos of the comments were published on Twitter by @Reagan Battalion, given Mr Yiannopoulos is the spearhead of the alt-right movement which came to prominence during the recent US election.

In response, the chairman of the American Conservative Union, Matt Schlapp, said Mr Yiannopoulos had been uninvited from CPAC where he was due to give a speech.

“We continue to believe that CPAC is a constructive forum for controversies and disagreements among conservatives, however there is no disagreement among our attendees on the evils of sexual abuse of children,” he said.

And soon after that, publisher Simon & Schuster announced it had cancelled the publication of Dangerous “after careful consideration”.

Mr Yiannopoulos said excerpts of the video that were shared online were misleadingly edited to remove the necessary context, and he was “horrified” by paedophilia.

“I am a gay man and a child-abuse victim. I would like to restate my utter disgust at adults who sexually abuse minors,” he said on Facebook.

But he also added that he was “partly to blame”.

“My own experiences as a victim led me to believe I could say anything I wanted to on this subject, no matter how outrageous,” he said.

“But I understand that my usual blend of British sarcasm, provocation and gallows humour might have come across as flippancy, a lack of care for other victims or, worse, ‘advocacy’.

“I deeply regret that. People deal with things from their past in different ways.”

The announcement that Mr Yiannopoulos would be a speaker at CPAC had already attracted controversy, given he hasn’t been shy about his provocative commentary.

CPAC is a big deal for conservatives; other speakers at the event this week will include President Donald Trump, Vice-President Mike Pence, Governor Scott Walker and Senator Ted Cruz.

Before the latest controversy, Mr Schlapp had said Mr Yiannopoulos’s invitation was about defending “free speech”:

We think free speech includes hearing Milo’s important perspective. #CPAC2017 pic.twitter.com/ssDS6HVmLN

— Matt Schlapp (@mschlapp) February 18, 2017

Critics now say that the fact that he was uninvited shows this was never the case:

https://twitter.com/JillFilipovic/status/833809927642705920?ref_src=twsrc%5Etfw

Mr Yiannopoulos’s $US250,000 ($A325,000) book deal had also been controversial: feminist writer Roxane Gay had withdrawn an upcoming book of her own from Simon & Schuster in response.

Last year, the Greek-born British writer was banned from Twitter for calling Ghostbusters actress Leslie Jones “barely literate” and a “black dude”.

Earlier this month, protesters at the University of California in Berkeley smashed windows and clashed with police in protest against his “Dangerous Faggot” college tour, forcing the cancellation of his appearance there.

The protests at Berkeley, California, against Milo Yiannopoulos earlier this month. Photo: Getty.

He responded on Facebook, saying, “Last night wasn’t a ‘protest’. It was a riot. A riot not a single prominent left-wing figure will denounce. This is what happens if you’re libertarian or conservative and you get too popular and influential.”

– ABC