When she was selected as the Conservative candidate for the Devon constituency of Totnes in 2009, after a groundbreaking public postal ballot, Sarah Wollaston hoped – perhaps optimistically – that it signalled the start of new era of open, positive politics. It isn’t entirely working out like that. Almost a decade after winning the seat, Wollaston is facing the threat of deselection courtesy of a barbed, insidious campaign by Brexiters.

In recent weeks, many of her Totnes constituents have received Facebook messages from the rightwing businessman and Ukip backer Arron Banks’s Leave.EU campaign, describing the MP as “Slippery Sarah” and urging supporters of Brexit to join the local Conservative association – and then deselect her. The “blue wave” campaign, as Leave.EU has dubbed it, has to be taken seriously. The Totnes association has seen a jump in applications for membership and Wollaston is preparing for a fight.

She can rely on the support of many. On market day in Totnes, the hilly town renowned as a centre of alternative cool in the south-west of England, most locals appeared to back her. Jacqi Hodgson, a Green party councillor, described the campaign against Wollaston as bizarre. “I have huge respect for the fact that Sarah is one of those politicians who put their constituents and the greater good first. We need politicians who are genuine. She’s grown into the job and got more and more outspoken.”

Jules, a single mother who declined to give her surname, said she had been hugely impressed with Wollaston when she went to her with a housing problem. “I’ve never voted Tory but I probably would next time just because of how kind and strong she is,” said Jules. “I think there’d be an outcry if they tried to get rid of her.”

Jonathan Cooper, a barrister who earlier this year lightheartedly launched a “Totnes passport” aimed at those who wished to remain a part of the EU, said the main point about Wollaston was that she was a very good local MP. He reeled off issues she had intervened in, ranging from racist graffiti to a road damaged by the “beast from the east” storm. “People would miss her and mind if she was forced out,” he said.

Pro-Brexit feeling is said to be strong in the fishing town of Brixham, in Wollaston’s constituency. Photograph: Brenda Melaniphy

Online, however, it is easy to find Wollaston critics apparently prepared to back the deselection plot. One, Jim, described himself as a moderate local Conservative voter but wrote on Facebook to Wollaston: “You can’t ride roughshod over your core Conservative vote, like me and not expect to face deselection.” Another, Jackie, said: “I am fed up of re-moaners wishing to disregard the result of the referendum we have already had on the grounds that people like me did not know what we voted for.”

At the beginning of the referendum campaign Wollaston was a Leave supporter but the former GP switched after the debacle of the bus slogans promising £350m a week to the NHS. In August she backed the idea of a people’s vote, arguing that the public had been misled by deliberate untruths during the Brexit campaign.

The move put her in the line of fire for the Leave.EU’s blue wave campaign. Others targeted include the former home secretary Amber Rudd, who has backed the idea of a people’s vote rather than no deal, and Anna Soubry, who champions a soft Brexit.

At the end of last month the blue wave sent attack ads to Devon in which it claimed: “54% in Totnes voted leave but Sarah Wollaston wants a second referendum ... Totnes deserves better than Slippery Sarah. Join the local Tories and deselect her.”

It got nastier during a rally at the Tory conference when Boris Johnson ally Conor Burns suggested the Brexit campaigner Darren Grimes, the founder of the campaign group BeLeave, should try for Wollaston’s seat, saying: “Have a look down in Totnes, you’d be brilliant.”

Burns and Grimes later brushed it off as a joke but Wollaston is certainly taking the threats seriously, claiming a “purple wave” – a reference to the Ukip colours – rather than a blue one was in danger of damaging the party.

“These ads are very poisonous,” Wollaston told the Observer. “It’s horrible, toxic stuff. It puts my association in a very difficult position. If people apply to join the party, they can’t turn them away without good reason.

“There has been a rise of membership in Totnes. If they want to make a challenge I’ll make my case and they can oust me if that’s what they want.” But Wollaston said it would be ironic if she was ousted because of a campaign by a one-issue group, having been originally chosen to stand in a public ballot in which everyone – regardless of political persuasion – was allowed to take part.

Leave.EU insists Wollaston and the others it is targeting are fair game. It says more than 230,000 people have viewed the ads and there have been almost 5,000 “click-throughs” to association websites.

I think Sarah should be held to account. She was elected on the Tory manifesto and that's not what she's doing now Ceri Jayes, Totnes Ukip branch chair

If Totnes is full of Wollaston supporters who don’t like the campaign, the fishing town of Brixham, also within the constituency, has a good few critics. Like many ports, Brixham is fiercely pro-Brexit. Ceri Jayes, the chairman of the Totnes Ukip branch, said: “You can cut the anger in Brixham with a knife.”

Jayes said she knew of five people who had joined the Tories to vote out Wollaston. “I really think Sarah should be held to account. She was elected last year on the Tory manifesto and that’s not what she’s doing now.”

Sally Lord, chair of the Brixham community partnership, was preparing for a meeting at which Wollaston was the star turn, alongside police chiefs discussing the number of bobbies on the beat and the problem of drones flying over people’s gardens. Asked what people thought of Wollaston and her current EU stance, Lord replied: “She is an excellent MP, very approachable, but Brixham is a big fishing port. Need I say more?”

Scallop fisherman Derek Meredith, one of those embroiled in the clashes with the French boats in the summer, filled in the gaps. He voted for Wollaston last time but does not plan to do so again. “People have voted for Brexit for good reasons,” he said. “It’s crazy for people to be saying we should stay in now. She’s not doing us any good; she should go – and the sooner the better.”

Ways to unseat an MP

Conservative

A Conservative MP who wants to be readopted as their party’s official candidate has to make a formal application well before an election. If he or she then fails to secure the backing of the executive council of the local party, which holds a vote, the sitting MP has the right to call a full postal ballot of all members of the local party. If the candidate does not secure the support of a majority of those members, he or she is deselected. Deselections are rare because Conservative MPs are normally assiduous at cultivating local support, though divisions over Brexit have created new tensions in some constituencies.

Labour

To get rid of a Labour MP who wants to stand again at a general election, a minimum of 33% of a constituency’s local Labour branches and affiliated organisations, including unions, must vote to remove him or her through the “trigger ballot” process. The threshold was reduced from 50% at party conference last month, making deselections easier to bring about. If that threshold is reached an open contest has to be held, in which other candidates as well as the sitting MP can stand. All local members vote in a secret ballot. The winner becomes the prospective parliamentary candidate, assuming Labour’s national executive committee rubber-stamps the decision.