The Liberal Democrats face a revolt from a local party over plans to replace a candidate who unilaterally stood down in a marginal Labour-held seat, saying he wanted to avoid the “nightmare” of handing the constituency back to the Conservatives.

Tim Walker announced in an article for the Guardian that although he did not trust Jeremy Corbyn on Brexit, he wanted to give Rosie Duffield, the Labour candidate who took Canterbury from the Tories for the first time in 2017 by just 187 votes, the best chance of winning.

Almost immediately afterwards, a party spokesman said Walker would be replaced “in due course”. Nominations for the 12 December election have to be finalised by Thursday afternoon.

But a local Lib Dem source said the party in Canterbury was vehemently opposed to replacing Walker and that all four members approved to stand as MPs had said they would not do so.

If, as seemed likely, the party instead imposed an outside candidate, they would find very little help from local members, the source said: “I think most activists would campaign in other seats rather than Canterbury. The poor unfortunate who is imposed will not find themselves in a very happy position. They will be met with, at best, ambivalence, at worst outright negativity.”

The source said that while they understood the desire of party officials to take on Labour, the situation in Canterbury was very particular. Duffield is strongly remain, and the Lib Dems received more than 4,500 votes in 2017.

Walker’s exit comes as the Lib Dem candidate in Boris Johnson’s seat, Uxbridge and South Ruislip, announced she was standing aside. Elizabeth Evenden-Kenyon said this was because of family illness and that the party would have enough time to select a new hopeful. The party said she would be replaced.

Writing in the Guardian, Walker, a journalist who formerly worked for the Daily Telegraph, said it had become clear that if he stayed in place in Canterbury, there was “a danger I’d divide the remainers” and allow victory for the Tory candidate, Anna Firth, a vehement Brexit supporter who worked with the Vote Leave campaign.

“I don’t trust Corbyn on Brexit, but I share with many members of my party locally a visceral dread of the Commons being filled with people like Firth,” Walker wrote. “Trying to stop that happening is now more important than ever, given Nigel Farage’s unholy alliance with Johnson.

“I’ve therefore asked that my local party withdraws my nomination papers to stand for Canterbury. Politics does not always have to be grubby and small-minded; sometimes it’s possible to acknowledge there’s something at stake that’s more important than party politics and do something that seems right.”

It was not an easy decision, Walker wrote, “but the nightmare that kept me awake was standing awkwardly at the count beside a vanquished Duffield as the Tory Brexiter raised her hands in triumph. I wanted no part in that.”

He added: “I now wish Rosie well and urge her to fight for our country and, when she hopefully gets to resume her seat in the Commons, to continue to think for herself.”

The Lib Dems are part of a so-called remain alliance, which has seen them, Plaid Cymru and the Greens give each others’ candidates a free run in 60 seats around England and Wales.

However, Labour has declined to take part in any pacts, while the Lib Dem leader, Jo Swinson, has been vehemently critical of Corbyn, saying she could not back him as prime minister.