Labour face a tricky test to hold the seat of Copeland, which will be left vacant when the incumbent MP, Jamie Reed, steps down to take up a post at Sellafield, the nuclear power plant that is the seat’s largest employer.

In addition to the political problems posed due to the Labour leader’s longstanding opposition to nuclear power, Labour’s biggest worry is if the Brexit effect, that has pulled away voters in both directions in the two post-referendum by-elections, persists into this by-election.

That has led some party strategists to consider attempting to recruit Ed Balls for the seat. He has a loose family connection as his father in law, the trade unionist Tony Cooper, hails from Whitehaven. But one ally of Balls described the idea that the former shadow chancellor would stand for the seat as “mad”, as it is difficult to reach both from London and from Yvette Cooper, his wife’s, constituency of Normanton, Pontefract and Castleford.

Instead, the leader’s office have found a candidate who they believe may have the stuff necessary to keep the seat: Rachel Holliday, the founder of Calderwood House, a homelessness charity. It was as a result of that work that Holliday was named as Cumbria’s Woman of the Year in 2015. That her husband, a police officer, works on Sellafield’s security only adds to her appeal as far as party strategists are concerned. Rival candidates say that she has been given advance sight of the party’s membership list.

Among her opponents for the seat: Thomas Docherty, the former Labour for West Dunfermline and Fife, who is from the party’s right, is preparing the ground for a bid for the seat. Also mulling a run is Lee Sherriff, who stood as the parliamentary candidate for the nearby marginal of Carlisle in 2015. Supporters of Sherriff believe that she is “battle ready” and therefore suited for a close by-election.She would also be a less divisive choice than Docherty, insiders believe.

The selection is an early test for the new and expanded leader’s office. Although Jeremy Corbyn himself was the victor in two landslides, the leader’s allies have been alarmed by the failure of pro-Corbyn candidates to win selections. Of the five by-elections in Labour-held seats since the start of the parliament, none have been taken by candidates from the Corbynite wing of the party.

This contest will be in more favourable conditions than previous selections, however. The post-Corbyn membership surge is no longer subject to a freeze date (new members must wait six months before voting in internal elections), and there is not a strong frontrunner from elsewhere in the party.