Winston Marshall has quit Mumford & Sons, blaming his “difficult decision” on an “unintentional Twitter storm”.

The banjoist and lead guitarist, 33, found himself at the centre of controversy after tweeting about US journalist Andy Ngo’s book, Unmasked: Inside Antifa’s Radical Plan To Destroy Democracy.

Marshall told his 10,000-strong following in March how he had read the “important” book, praising Ngo as a “brave man” in a now-deleted tweet.

Critics of the book, which claims to expose a “violent extremist movement”, say it inflates the size and threat of the left-wing antifa movement, which was a frequent target of Donald Trump.

Announcing he would quit on Thursday, the musician posted online how being in Mumford & Sons had been “exhilarating”, describing how he had been a “lucky boy”.

And he said it was a “blessing” to work alongside fellow members Marcus Mumford, Ben Lovett and Ted Dwane.

“Every gig was its own adventure. Every gig its own story. Be it odysseys through the Scottish Islands, or soapbox shows in Soho,” he said.

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He added: “Who in their right mind would willingly walk away from this?

“It turns out I would. And as you might imagine, it’s been no easy decision.”

Marshall said he believed his tweet to Ngo was “innocuous” – but within 24 hours it was trending with “tens of thousands of angry retweets and comments.”

“I’ve had plenty of abuse over the years. I’m a banjo player after all. But this was another level.”

And he told how his bandmates and friends also came under fire from the “viral mob” – adding how he “regrets very much” the “distress” they endured.

Explaining his tweet about Ngo’s book, Marshall insisted: “The book documents the recent activities of the extreme Left in the US.

“The tweet was misconstrued by many as an endorsement of the equally abhorrent Far-Right. Nothing could be further from the truth.

“I condemn unequivocally all political extremism, be it of the Right or Left.”

“I’ve spent much time since reflecting, reading and listening. I know now that, as long as I am a member of the band, speaking my mind on the evils of political extremism could bring them trouble. My loyalty and love for them cannot permit that.

“However to remain in the band and self-censor will gnaw my conscience, erode my integrity. By leaving I hope to speak freely without them suffering the consequences.”

Marshall, whose father is British investor Sir Paul Marshall, told how he was looking forward to “new creative projects” and speaking and writing “on a variety of issues”.

He will also remain involved in the Hong Kong Link Up, a non-profit organisation which he co-founded, which links British residents with people from Hong Kong arriving in the UK.

Marshall also thanked the band, which formed in London in 2007, describing their adventure together as the “ride of a lifetime.”