London (CNN) Early one Sunday morning, British politician Heidi Allen answered her front door to be confronted by a man who had been harassing her.

He was a former soldier, whom she had met at a local remembrance service in her village in eastern England, who began to email and tweet at her to the point where she was forced to block him.

"He tried to thrust his war medals into my hands, [saying] 'take them back, give them back to the Prime Minister, I don't want them,'" before going into an aggressive spiel about Brexit, Allen told CNN.

Allen was then a Conservative MP, before quitting the party in February to stand as interim leader of the new anti-Brexit party Change UK. This week she joined the Liberal Democrats, who are also opposed to Brexit.

While Allen's office warned the man not to approach her or visit her private house again, he then shared aerial images and detailed information about her home to what she said was his "hard Brexit, right-wing network."

But what particularly frightened Allen, she says, was a reference he made about buying a rope. "It was absolutely terrifying," Allen recalls. "I was really, really, really scared."

The man, Ian Couch, was eventually jailed for his threats -- but his effect on Allen's life remains. Permanent panic buttons, security lights and industrial locks are now installed around her house.

"You shouldn't have to live like that," Allen says, "but, it's normal now."

This is a reality not just for Allen, but many other British lawmakers, who are receiving an unprecedented number of threatening messages since the UK's vote to leave the European Union in 2016.

Heidi Allen installed permanent panic buttons and security lights after she was targeted.

MPs are now taking extra security measures -- including taking taxis home and carrying panic alarms -- to feel safe while doing their jobs in a polarized political climate.

Since the 2016 referendum, MPs have faced abuse on social media and in person for their stances on Brexit.

Women on the front line of British politics have experienced a particularly unnerving level of abuse, ranging from harassment to outright threats of rape and murder.

The memory of Labour MP Jo Cox , who was stabbed and shot to death by a far-right extremist after a public meeting in 2016, however, reminds many of how very real those threats can be.

Cox was the first British lawmaker to be killed in office since a Conservative MP was killed by an IRA car bomb in 1990.

Jo Cox, 41, was shot and stabbed in her constituicency.

Earlier this year, London Metropolitan Police chief Cressida Dick told a parliamentary committee that officers had seen a "very considerable rise" in the number of threats received by MPs.

Police statistics showed crimes committed against MPs had more than doubled from 151 in 2017 to 341 in 2018.

"A lot of those threats are very real," Alice Lilly, a senior researcher for British think tank the Institute for Government, told CNN. "We have seen several people prosecuted for sending threats, we've seen somebody prosecuted for plotting to murder a serving MP -- so these are very substantial threats."

Research by the University of Sheffield , which analyzed 8 million tweets to and from MPs in the first six months of 2019, found that the most dominant topics were Brexit, democracy and Europe, with Brexit attracting the most abusive replies.

Females and MPs from minority backgrounds 'disproportionately targeted'

Labour MP Tracy Brabin , who was elected in Cox's seat after her murder, told CNN there is "no doubt that women and BAME (Black, Asian and minority ethnic people) MPs get more abuse than men, but men are also targeted -- and also across the political spectrum."

Researchers from The Institute for Government also found in their analysis of police data that female MPs and those from minority backgrounds are "disproportionately targeted."

Following Jo Cox's murder, Tracy Brabin was elected as Labour MP for Batley and Spen.

When Brabin was elected as MP for Batley and Spen in 2016, she says she made a conscious decision to ensure she was more accessible to her constituents than any other MP.

"The two women who were with Jo when she was murdered became my staff members," Brabin explains, "and I said to them if we hide away -- if I can't walk to get a sandwich, if I can't get a newspaper without protection, if I can't go to a lunch club without having someone with me, we've failed."

"My family were concerned," she admits, "but my real belief is lightning doesn't strike twice, but if I hide away they win. If it looks like it's affected me, it's a magnet for more because you're the victim."

While Brabin says she received "very little abuse" when she first became an MP, she has noticed an increase since UK Prime Minister Boris Johnson started referring to the Benn Act as the "surrender bill."

That legislation, which was passed as law by Parliament on September 9, aims to prevent the UK from crashing out of the European Union without a deal and requires Johnson to ask for a delay if no Brexit deal is agreed with the EU by October 19.

"In the last few weeks it has escalated and we've had for the first time threatening phone calls, threats to push me down the stairs, to drive me over with a car... But I'm not afraid. I'm not taking it too seriously," Brabin said.

In fact, Brabin says the frustrating thing is the hours her staff spend sifting through "vile abuse" on her social media channels -- 75% of which she says comes from people outside of her constituency.

"It's anti-democratic because it stops good local people from engaging with me. All you get is one voice, and one tone, coming from all over the country."

Boris Johnson's rhetoric is 'fueling hatred'

With words like "surrender," "enemy," and "betray," Johnson recently has come under fire by MPs for spurring on hatred within the UK.

In a statement to CNN, a spokesperson from Downing Street said: "The PM has been clear that threats and abuse against MPs are totally unacceptable and that no MP or anyone else in public life should face threats or intimidation."

However, Johnson provoked particular fury in the House of Commons at the end of September with his response to concern over threats and his suggestion that "getting Brexit done" would be the best way to honor Cox

The UK's Prime Minister Boris Johnson has been criticized for using language that could contribute to the spreading of hate throughout the country.

"Many of us in this place are subject to death threats and abuse every single day. Let me tell the Prime Minister that they often quote his words -- surrender act, betrayal, traitor -- and I, for one, am sick of it," Labour's Paula Sherriff said in Parliament to Johnson, who then dismissed it as "humbug."

Labour's Jess Phillips, who has spoken frequently about the abuse she has suffered as an MP and has admitted to carrying a panic alarm with her, also criticized Johnson for his language by tweeting a photo of a threatening letter she received at her office.

"This week I received an anonymous letter to my constituency office," Phillips tweeted. "@10DowningStreet might think we are "humbugs" about his words but they are literally being used in death threats against me."

The letter referenced the phrase "I would rather be found dead in a ditch" that Johnson used when he was asked if he would extend the Brexit deadline. The anonymous writer warned: "This is what will happen to those who do not deliver Brexit."

This week I received an anonymous letter to my constituency office here is what it said. @10DowningStreet might think we are "humbugs" about his words but they are literally being used in death threats against me. pic.twitter.com/au6E0v9CpI — Jess Phillips Esq., M.P. (@jessphillips) September 25, 2019

Johnson later defended the language he used in Parliament, but apologized if lawmakers had misunderstood his use of the word "humbug" in response to their concerns.

"My use of the word humbug was in context of people trying to prevent me -- us -- from using the word 'surrender," he told the BBC. "I can certainly say sorry for the misunderstanding."

Brabin told CNN, however, that Johnson's language was helping "fuel hatred" and because anxiety is high among constituents, "the voice of panic and fear is heard louder."

"The Prime Minister has an incredibly loud voice with a massive reach and he leads the way -- his tone filters down," she says, adding that as a result "the misleading comments from Number 10 are picked up and regurgitated."

While Allen agrees that the abuse MPs receive has escalated since the Brexit vote, she says social media is the main driver behind the increase -- especially as people believe they can hide under the cover of anonymity.

"I don't think it's just Brexit," Allen said. "Social media gives fast, hidden, easy access to public figures in a way that I suspect didn't exist for MPs in the past, and you can be anonymous -- or you think you can."