The Conservatives are expected to retain the Sleaford and North Hykeham seat as voters go to the polls in the Lincolnshire by-election on Thursday (8 December). But Westminster watchers will be keeping a close eye on how Ukip's Victoria Ayling and Labour's Jim Clarke perform.
New Ukip leader Paul Nuttall has promised to take on Labour in their north of England heartlands and become the "patriotic voice of working people". His predecessor Nigel Farage visited the seat on Monday to drum-up support for Ayling and press home the party's pro-Brexit message.
"People here voted for Brexit and this is about getting the right deal, which you won't get if people vote Conservative," he said.
The by-election was triggered when fellow Eurosceptic and former Tory MP Stephen Philips quit the House of Commons in November over the government's handling of the UK's split from the EU.
The barrister wanted MPs to have a greater say in the process before Article 50, the mechanism to break from Brussels, was triggered.
Conservative candidate Dr Caroline Johnson is defending his majority of more than 24,000 votes from the general election.
"I am the only person who can support the prime minister and the government to deliver Brexit," she said. "I am completely behind the government's plans for Brexit and to deliver on the decision made by the British people."
Residents in North Kesteven, which makes up part of the Sleaford and North Hykeham constituency, voted by more than 62% for a Brexit at the EU referendum in June.
Labour, who have vowed to put down an amendment to any Article 50 bill in the Commons, secured a second place and more 17% of the vote in Sleaford at the general election.
But Clarke could be overtaken by Ukip, who came third in the seat with almost 16% of the vote last May.
The vote comes after the Richmond Park by-election on 1 December. Liberal Democrat Sarah Olney overcame Zac Goldsmith's 23,000 majority to win the west London seat.
Like Sleaford, Brexit became a major issue on the doorstep after 69% of Richmond-upon-Thames residents backed Remain.
Goldsmith, the former Conservative MP who quit parliament in protest over the government's decision to back a third runway at Heathrow Airport and stood as an independent, campaigned for a Brexit.
The latest by-election is being held on the final day of the government's appeal to the Supreme Court over Article 50. The High Court ruled in November that MPs must have a vote on the issue. A final decision is expected in January 2017.