The husband of murdered British MP Jo Cox said he was "sickened" after the prime minister urged politicians to "honour" her memory by delivering Brexit.
It came as Boris Johnson returned to the UK for a showdown with politicians after the Supreme Court ruled his suspension of Parliament was unlawful.
Opposition MP Jo Cox, 41, was murdered a week before the 2016 Brexit referendum by Thomas Mair, a loner obsessed with Nazis and extreme right-wing ideology. She had campaigned to remain in the EU.
Following Mr Johnson's comments, her husband Brendan Cox tweeted that he "felt sick".
"The best way to honour Jo is for all of us (no matter our views) to stand up for what we believe in, passionately and with determination," he added. "But never to demonise the other side and always hold onto what we have in common."
Feel a bit sick at Jo’s name being used in this way. The best way to honour Jo is for all of us (no matter our views) to stand up for what we believe in, passionately and with determination. But never to demonise the other side and always hold onto what we have in common.
— Brendan Cox (@MrBrendanCox) September 25, 2019
Her sister Kim Leadbeater said he was "wrong" to use her sister's name.
"To use Jo's name in that way was wrong. People want an end to this chaos, it was a very heated debate and under those circumstances people do make mistakes. I hope he has sometime to reflect on it and maybe know it was not the best possible thing to say."
Mr Johnson said threats to MPs, in particular against women, were deplorable.
Even Rachel Johnson, the prime minister's sister, slammed the comments and said they were "a very tasteless way of referring to the memory of a murdered MP" who had campaigned against Brexit.
After returning from the United Nations conference in New York early, Mr Johnson faced his critics head on as he threw down the gauntlet urging them to call for a vote of no confidence in him - had they successfully done so a general election would have been triggered.
Two previous attempts by him to call for a snap election have been defeated.
Mr Johnson told them: "I think the people of this country have had enough.
"This Parliament must either stand aside and let this Government get Brexit done or bring a vote of confidence and finally face the day of reckoning with the voters."
Despite the leader of the opposition Jeremy Corbyn describing Mr Johnson as "dangerous" and urging for his resignation, they declined his offer.
Mr Corbyn had said that “for the sake of this country he should go”, but refused to agree to an election until he “gets an extension” to Brexit.
It led to Mr Johnson accusing them of “political cowardice”.
He added: “The people outside this house understand what is happening … The leader of the opposition and his party don’t trust the people.”
The raucous session in the House of Commons came after the UK Supreme Court’s landmark declaration on Tuesday that his suspension of Parliament for five weeks ahead of the Brexit deadline was unlawful.
Mr Johnson told Parliament the court's decision was "wrong" and accused politicians of "sabotaging" Brexit negotiations.
He said: "Instead of facing the voters the opposition turned tail and fled from an election. Instead of deciding to let the voters decide, they ran for the courts … it is absolutely no disrespect to the judiciary to say I think the court was wrong.”
After the court ruling Sterling dropped the most in nearly a month on Wednesday.
Mr Johnson was also criticised for using inflammatory language such as “surrender” and “betrayal” by opposition MP Paula Sherriff who pleaded with him to refrain from using "dangerous" words.
He had used the word "surrender" to describe legislation passed earlier this month which aims to block a no-deal Brexit.
Mr Johnson retaliated by saying: "I have to say, Mr Speaker, I've never heard such humbug in all my life."
On Thursday, the Prime Minister said he deplored any threats to MPs and added in an interview with the BBC: "But I do think in the House of Commons it is important I should be able to talk about the surrender bill, the surrender act, in the way that I did."
Mrs Cox's sister added that she was left "dumbstruck" by the debate and also criticised his use of the word "humbug" in response to the issue.
Speaker of the House John Bercow criticised MPs on Thursday saying the culture in Parliament had been "toxic" and the worst he had seen in 22 years.
The government faced another setback when MPs rejected a move for a three-day parliamentary recess next week.
