Nigel Farage was branded a "Putin-loving free speech impostor" by a US congressman as he appeared at a meeting on civil liberties in Washington.
Democrat representative Jamie Raskin accused the Reform UK leader of being a "Trump sycophant" at the US House Judiciary Committee on Wednesday.
Mr Farage skipped Prime Minister's Questions (PMQs) in Britain to give evidence on civil liberties in Washington and voice concerns about freedom of speech.
Mr Raskin said: "He should go and advance the positions he's taking here in Congress today, in Parliament, which is meeting today, if he's serious about it.
"To the people of the UK who think this Putin-loving free speech impostor and Trump sycophant will protect freedom in this country, come on over to America and see what Trump and MAGA [Make America Great Again] are doing to destroy our freedom... you might... think twice before you let Mr Farage make Britain great again."
The hearing comes after after Father Ted co-creator Linehan was arrested at Heathrow on Monday on suspicion of inciting violence over a series of gender-critical posts on the social media platform X.
The Irish comedy writer, 57, alleges that he was detained by five armed officers immediately after he stepped off a plane from Arizona.
High-profile figures have condemned the arrest, including Harry Potter author JK Rowling who labelled it “utterly deplorable”.
Mr Farage raised the case and that of Lucy Connolly, who was jailed for stirring up racial hatred against asylum seekers over a tweet in the aftermath of the Southport murders last year, during the hearing.
"It doesn't give me any great joy to be sitting in America and describing the really awful authoritarian situation that we have now sunk into," Mr Farage said.
He claimed US tech chiefs could face arrest when entering the UK as he criticised the treatment by police of Linehan.
Speaking of the Irish writer’s arrest, the Reform UK leader told the US House Judiciary Committee: “He put out some tweets months ago when he was in Arizona, and months later he arrives at Heathrow Airport to be met by five armed police…
“This could happen to any American man or woman that goes to Heathrow that has said things online that the British Government and British police don’t like.
“It is a potentially big threat to tech bosses, to many, many others.”
He added: “At what point did we become North Korea? Well, I think the Irish comedy writer found that out two days ago at Heathrow Airport.”
Mr Farage warned that the Online Safety Act “will damage trade between our countries, threaten free speech across the West because of the knock-on rollout effects of this legislation from us or from the European Union”.
Of Connolly's social media post that lead to her guilty plea and imprisonment, he said: "It was intemperate, it was wrong, but she removed it three-and-a-half hours later. Sentenced to 31 months in prison. She's now out, having served 40% of the time.
"I wanted to bring her with me today as living proof of what can go wrong.
"Sadly, the restrictions that have been put on her banned her from making the trip, which is a very, very great shame."
Ahead of the meeting, Mr Farage denied suggesting that the US potentially impose trade sanctions on countries over freedom of speech.
"I have not suggested that for one moment. That is the interpretation of the prime minister, who is very much on the back foot," he told Sky News.
Pressed on what he did say, the Reform UK leader said: "I've said that I hope that American political parties, leaders and businesses have a frank conversation with the British government and say, 'if you don't sort this out, it's going to have serious trade implications for both of us."'
Asked if there was "hypocrisy" in him speaking on the topic in the US amid a crackdown on free speech in that country, he said: "Even more reason for me to be here to say, look, we've gone way down this path. Be vigilant in this country."
He added: "I'm not saying Trump's gone a bit far. I'm here to talk about what's happening in the United Kingdom."
