UK spending on security for MPs topped at least £4.2 million ($5.2 million) in the latest data available, continuing its climb since Labour MP and Remain campaigner Jo Cox was killed by a far-right extremist days before the June 2016 Brexit referendum.

Yesterday, Labour MPs invoked Cox’s memory, with Paula Sheriff calling on prime minister Boris Johnson to stop using words like “surrender” and “betrayal” when discussing Brexit. She said that language was being echoed in the harassment and death threats lawmakers face.

Johnson retorted that he’d “never heard such humbug in all my life,” which sparked a furious reaction among the opposition.

He then responded to Labour MP Tracy Brabin’s invocation of Cox. “The best way to honor the memory of Jo Cox and indeed the best way to bring this country together would be, I think, to get Brexit done,” he said.

Brendan Cox, the husband of the late politician, said he felt “a bit sick at Jo’s name being used in this way.”

Threats against MPs have reportedly surged since the Brexit vote. In addition to the 2016 to 2017 period, spending also grew from 2017 to 2018, after a March 2017 terror attack outside parliament left six people dead.

The head of the UK’s Metropolitan police said earlier this year that the number of threats and harassment directed at MPs is now “unprecedented.” The police chief cited a polarized political climate as a driving force behind the uptick, and said women and non-white MPs were at particular risk.

After Johnson’s comments yesterday, leader of the pro-Remain Liberal Democrats Jo Swinson told the House that she had reported a death threat against one of her children to police.

“I cannot overstate the frequency by which I have been informed over the last year or so by members on both sides of the House and on both sides of the Brexit argument of the fact and persistence of threats they have received,” said John Bercow, speaker of the House.

Bercow today said that the tone of dialogue in parliament yesterday was worse than any in his 22-year parliamentary career. He called on MPs to “lower the decibel level” and to not behave as enemies.