Johnson replied: “I think, Mr Speaker, I have to say, Mr Speaker, I have never heard such humbug in all my life”, sparking utter fury on opposition benches.
Bercow was forced to intervene on numerous occasions before finally urging MPs on all sides to “weigh their words”.
“I am keenly conscious of the fact that there are members on both sides of the House and indeed on both sides of the Brexit argument who have been personally threatened and whose families have been threatened,” he said.
“I have stated very publicly my revulsion at such behaviour whether it has affected members on one side or the other, people who are anti-Brexit or members who are pro-Brexit whose families have been wrongly threatened or whose parents have been abused in their presence.
“And I would simply appeal to responsible colleagues in all parts of the House to weigh their words.”
Later, Brabin said: “As the woman who has taken over a seat left by our dear friend Jo Cox, can I ask him in all honesty as a human being please, please will he going forward moderate his language so that we will all feel secure when we’re going about our jobs.”
Johnson replied: “Of course there will be an attempt to try to obfuscate the effect of this Act, but it does – the capitulation act, or the surrender act or whatever you want to call it – it does, I’m sorry, but it greatly enfeebles, it greatly enfeebles this government’s ability to negotiate.
“But what I will say is that the best way to honour the memory of Jo Cox and indeed the best to bring this country together would be, I think, to get Brexit done.”
Outside the chamber, Liberal Democrat leader Jo Swinson described Johnson as an “utter disgrace”.
Matthew McGregor, of Hope Not Hate, said: “The prime minister’s behaviour in parliament this evening has been appalling.
“His language has been inflammatory. His rhetoric risks real world consequences.”