Their supporters have previously called for riots at demonstrations supporting Mr Johnson, amid warning that his language was “calling to” nationalists.
Robinson’s official channel on the encrypted messaging app Telegram shared a post mocking warnings that MPs were receiving death threats.
The English Defence League founder called on his followers to “back Boris” and characterised him as a champion “for the people” versus “traitors in parliament”, and “corrupt elite scumbags”.
Robinson’s supporters heaped praise on the prime minister in a series of comments, with one writing: “Go Boris, f*** the lot of them scumbag traitor bastards.”
Another commenter wrote: “F*** them all Boris, respect to you.”
The anti-Islam Democratic Football Lads Alliance accused “corrupt and evil” MPs of “taking orders from a foreign power”.
A Facebook post attacked Labour MPs for bringing up Ms Cox’s death, adding: “We aren’t disgusted by the word ‘humbug’. We are disgusted by you, you utter c***s. Not by [Mr Johnson].”
Britain First and its former deputy leader Jayda Fransen were sharing clips of Mr Johnson’s appearance in parliament on Wednesday evening, showing him accuse Jeremy Corbyn of wanting the “entire country to be held captive in the EU”.
Supporters of the extremist group called for no-deal Brexit “or a revolution”, while users of a separate Telegram channel for British “patriots” celebrated Mr Johnson walking out of the House of Commons.
Hopkins, a far-right activist who called refugees “cockroaches” and called for a “final solution” after the Manchester attack, called his performance “utterly brilliant”, writing on Twitter: “MPs complaining about being called TRAITOR – it’s because you betrayed the people and you betrayed democracy in the UK.”
In a flurry of activity on Wednesday night, extremists across social media platforms labelled MPs “traitors” and called for “no surrender”.
Mr Johnson called the law passed by parliament to prevent the UK crashing out of the EU without a deal next month a “surrender act” 14 times during the heated House of Commons debate.
Echoing conspiracy theories frequently shared by right-wing extremists, he accused MPs who supported the law of lying about their intentions and attempting to stop any kind of Brexit.
“The people of this country can see perfectly clearly what is going on,” the prime minister said. “The people at home know that this parliament will keep delaying and it will keep sabotaging the negotiations, because members do not want a deal.”
He later claimed that the opposition wanted to “betray the people”.
Labour MP Paula Sherriff called on Mr Johnson to stop using pejorative language to describe a law passed by the majority of MPs.
“Many of us in this place are subject to death threats and abuse every single day,” she added, reminding MPs that they sat under the shield of murdered MP Ms Cox.
“Let me tell the prime minister that they often quote his words – surrender act, betrayal, traitor – and I, for one, am sick of it. We must moderate our language.”
Mr Johnson replied: “I have to say that I have never heard such humbug in all my life.”
Ms Cox was murdered days before the EU referendum by a white supremacist, who saw her as a “traitor” because of her support for the Remain campaign and refugees.
Labour MP Lucy Powell told the House of Commons that the murder “did not happen in a vacuum”.
“This is the kind of language and the context that led to the murder of an MP leaving her surgery of an evening in a small market town by somebody from the far right,” she added.
The call for moderation was repeated by several MPs including Labour’s Rachel Reeves, who condemned the “dangerous language of betrayal and surrender, which sows division and worse in the communities we all serve”.
Conservative Jeremy Lefroy said the majority of MPs wanted to leave the EU with a favourable deal and warned: “With freedom of speech, on which we fully agree, comes responsibility, and sometimes that responsibility means not saying what one might like to say – words like ‘surrender’, ‘betrayal’ and ‘treason’.”
Experts have said the prime minister and some other pro-Brexit politicians are “using the language of the far right” and playing into extremist narratives.
Chloe Colliver, who leads the digital research unit at the Institute for Strategic Dialogue think-tank, said that by using the phrase “surrender bill” and positioning himself as enacting the “will of the people”, Mr Johnson was “calling successfully to a nationalist interpretation of the Brexit debate”.
“It seems very purposeful to me and it really harks back to the Second World War nostalgia in this debate, which plays powerfully to the far right and nationalist groups,” she previously told The Independent.
Senior police officers have repeatedly called for politicians and other public figures to avoid worsening tensions around Brexit with inflammatory language.
Martin Hewitt, chair of the National Police Chiefs’ Council, issued a warning over the “incredibly febrile atmosphere” as police are brace for potential unrest next month.
Reports of abuse and death threats towards MPs have been rocketing, with Metropolitan Police commissioner Cressida Dick describing the scale and ferocity of attacks as “extraordinary”.
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