A three-way battle will take place tonight to select Labour’s Parliamentary by-election candidate.

Hospital campaigner Rachel Holliday, Copeland councillor Gillian Troughton and Allerdale councillor Barbara Cannon will fight for party members’ votes in Egremont Market Hall to get the nod in the race to succeed outgoing MP Jamie Reed.

Labour’s selection process has already been mired in controversy amid reports that the influential GMB union will refuse to back Mrs Holliday, should she win tonight’s vote, after its preferred candidates failed to make the final shortlist.

A source said that the GMB, which has backed Labour’s Copeland seat since the 1930s, is “furious” at the decision of the party’s national selection panel to overlook Cumbria county councillor Tim Knowles and former Dunfermline and West Fife MP Thomas Docherty for its shortlist.

It is understood that eight were originally shortlisted and it was whittled down to the final three last Friday.

It has been claimed in the national press that Mrs Holliday is party leader Jeremy Corbyn’s preferred choice to contest the by-election.

The source added that the selection panel of Labour’s ruling National Executive Committee (NEC) – made up of Kate Osamor, the Shadow Secretary for International Development, Jennie Formby, the Unite union’s political director and Christine Shawcroft, the new director of left-wing movement Momentum – “clearly did not want the GMB’s candidate to win the selection”.

It is understood that Coun Knowles, a county councillor for Cleator Moor East and Frizington, is now considering his position as chairman of Labour’s Cumbria Campaigns Forum as a result of the fall-out.

He said: “If what my friends in the GMB are saying is true, then it seems myself and Mr Docherty were wasting our time entering the contest in the first place.”

However, a number of local GMB members have come out in support of Mrs Holliday.

Sellafield shop steward Edwin Dinsdale and Carl Lewthwaite, who sits on the GMB’s National Equality Forum, have thrown their weight behind her campaign.

Mr Dinsdale said: “The nuclear industry and the Sellafield site are facing some really challenging times.

"We need a strong Labour candidate to fight our corner and I am convinced that Rachel is that person.”

Mrs Holliday, who is part of the We Need West Cumberland Hospital campaign group, is the driving force behind Egremont’s Calderwood House homeless hostel.

Mrs Holliday, who lives in Hensingham, said: “We have already taken the fight for our hospital to Westminster, met Government officials and told them what we need.

“Now I’m seeking the support of the local Labour Party and the people of Copeland, so I can continue our campaign in Parliament and speak up for our people full-time.”

Gillian Troughton, of Moresby Parks, an active Remain campaigner in last year’s EU referendum, said: “I believe I can protect public services like the West Cumberland Hospital, for which I have been a great campaigner over the years. I am also a champion for low-carbon resources, including nuclear.”

Mrs Troughton, 51, was elected to Copeland council in 2011 and won her seat on Cumbria County Council, representing Howgate, in October 2015.

Mrs Cannon, from Harrington, has had a 25-year career in politics, including a 16-year stint on Cumbria County Council, and currently sits on Allerdale council.

Mrs Cannon stood as her party’s Parliamentary candidate for Penrith and the Border seat in the 2010 election.

“I have a good track record in campaigning on the issues that matter to people,” she said.

“I’m a proud west Cumbrian and it’s crucial that west Cumbria has a united, strategic vision of what it wants to be. Our strength is in our community.”

Mr Reed will step down at the end of January for a job at Sellafield.

However, Labour – as the party that currently holds the seat and is likely to move the writ that triggers the by-election – has suggested that May 4 may be its preferred date.

The Liberal Democrats have become the first party to publicly confirm their Copeland by-election candidate.

The party has selected Rebecca Hanson, a Cockermouth town councillor, who has been an outspoken opponent of the Success Regime’s plans to overhaul NHS services in West Cumbria.

A former maths teacher, Mrs Hanson says she feels compelled to put her name forward for selection, adding that it was partly her background – being given a chance to be educated at Cambridge after starting with no prospects at a rough school in Newcastle – that has given her a sense of calling.

“I was given a chance. I have dedicated my life to looking after society because I was given that opportunity for free,” she said.

Mrs Hanson has worked with the Lib Dems nationally to help shape its education policies. In 2013, she joined Brigham Parish Council and more recently was elected to Cockermouth.

Fighting for health services, flood prevention measures, the economy, and against a hard Brexit would be top of her agenda if elected, she says.

The Conservatives , while campaigning locally, have yet to formally launch their selection process, adding that it will begin once Mr Reed’s resignation takes effect.

A spokesman said: “Mr Reed hasn’t officially resigned as an MP yet, so the polling day hasn’t been announced but we will be selecting in due course.

“We’ll be selecting someone who’ll be a great local champion and have a plan to protect local jobs and industry and improve infrastructure to boost the region’s economy.”

UKIP ’s West Cumbrian branch has selected Fiona Mills as its candidate.

Ms Mills, chairman of UKIP Cumbria who stood for the Carlisle seat in the 2015 election, must now have her selection ratified by the party’s national executive committee.

The Green Party has confirmed that it will field a candidate on “an anti-nuclear and anti-poverty campaign”, and will make a selection on January 24.

Allan Todd, who stood for Copeland in the 2015 General Election, has confirmed that he is not in the running.