Politicians fighting the general election have been told to take unprecedented security precautions by their parties and police. Those seen as most at risk are being equipped with security alarms amid fears that a winter poll dominated by Brexit could turn violent.

Many have also been advised not to campaign after dark or alone, and not to enter people’s homes even if the weather is bad, as the country heads towards what is expected to be the most fiercely fought and unpredictable election in recent times.

On Saturday the former Conservative MP Antoinette Sandbach, a prominent Remainer who was stripped of the whip by Boris Johnson in September and last week defected to the Liberal Democrats, told the Observer she had been equipped by parliament with a security device that triggered an immediate armed police response in the event of an incident.

Sandbach, who will contest the seat of Eddisbury in Cheshire, said: “I am not going to be put off campaigning by threats and online trolls. But we do have to take measures to ensure our safety.” She added that Cheshire Police had recently issued guidance to all MPs and candidates in the area about how to campaign safely, which included the need for them to be accompanied by at least one party worker at all times.

Labour MP Luke Pollard, whose parliamentary office in central Plymouth has been attacked on two recent occasions by vandals, said that he and his staff would all be carrying personal attack alarms following advice from party bosses.

“I will be carrying it at all times. It has a button that you press that connects to a network where an operator will listen in immediately wherever I am,” Pollard said. “When you press it you’re supposed to say things like: ‘Put the knife down’ or ‘Please don’t point that at me’ or ‘What are you doing in my house?’ and the operator can coordinate the response.”

MPs last week voted to hold the first winter election since February 1974, less than a fortnight before Christmas, in order to break the parliamentary deadlock over Brexit.

But many MPs and candidates are privately dreading knocking on doors in the dark, knowing they will be confronted by intense anger over Brexit. One Labour MP from a Leave seat in the Midlands said: “It will be awful, as it will be on almost every doorstep. People saying ‘we voted for Brexit in 2016. Why have you not delivered?’”

The latest Opinium poll for the Observer suggests Brexit will be uppermost in voters’ minds. While many cite the NHS as a more important issue, 40% name Brexit as the main issue affecting their vote, against 18% for the NHS.

The Labour MP for Batley and Spen, Tracy Brabin, said she and her team had discussed campaign safety measures in a meeting with councillors on Friday, including her campaign co-ordinator who was a close friend of Jo Cox, the Labour MP murdered by a rightwing extremist days before the 2016 Brexit referendum.

A decision was taken to avoid campaigning on the streets of Brabin’s constituency, in west Yorkshire, from 5pm onwards. “Nobody’s campaigning at night,” Brabin said. “In the evenings we’ll probably be doing a lot of phone banking; we’re just going to have to be a lot more cautious because people are cross.”

Paula Ferguson, the Liberal Democrat candidate in Winchester, Hants, said her party was reinforcing the advice that MPs should not campaign alone, particularly in the dark. Although she did not feel in danger she said that she would be wary of entering people’s homes. “I do not feel like I am in danger – but we did not think Jo Cox was in danger,” Ferguson said.

Boris Johnson was widely criticised in September for appearing to dismiss as “humbug” MPs’ concerns over their safety.

Last week the culture secretary Nicky Morgan and the former home secretary Amber Rudd joined a growing number of Conservative moderates who have announced they will not stand for election.

Morgan, who was a strong Remainer but joined Johnson’s cabinet because of her belief that delivering Brexit with a deal was the only way forward, said “the clear impact on my family and the other sacrifices involved in, and the abuse for, doing the job of a modern MP” was part of the reason for her decision.

Brabin added: “My problem is that I love chattering. Sometimes I get left behind (on doorsteps). I’m not saying that I’m nervous of the electorate. What I’m saying is that I don’t want my volunteers to be put into positions where they feel uncomfortable.”