CLACTON-ON-SEA, United Kingdom - A vote in the seaside town of Clacton on Thursday was set to shake up British politics by securing the anti-EU UK Independence Party (UKIP) its first seat in parliament.
Officials began counting ballots after polling stations closed and the result was expected in the early hours of Friday.
The populist party, which came first in European Parliament elections, also campaigns against mass immigration and has repeatedly defended itself against accusations of racism.
Lawmaker Douglas Carswell defected from Prime Minister David Cameron's Conservative party to UKIP in August, and looks set to comfortably retain his seat on the southeast English coast.
Carswell told reporters in the town that UKIP was "a proper political party that's democratic, owned by its members and full of ordinary people, not career politicians."
"It feels incredibly invigorating," he said.
Once a fringe party, UKIP's support has been steadily growing for years and it scored better than all other parties in European elections in May, taking 27 per cent of the vote on the back of growing disillusionment with the mainstream political parties.
But it has yet to win a seat in the House of Commons - a major breakthrough that UKIP leader Nigel Farage is confident will be achieved in the early hours of Friday morning when the Clacton results come in.
Farage said that joining the British parliament would bring about "the single biggest change of perception that we need".
"To be in Westminster gets rid of our biggest electoral problem, which is people say: 'Ok Nigel, I agree with you, mate, but there's no point voting for you because you can't win'".
The party says a first seat in parliament would be a huge boost ahead of the May 2015 general election, where it is hoping to win several more.
Another Conservative MP, Mark Reckless, followed Carswell in defecting to UKIP last month although pundits suggest he will face a tougher challenge to hold onto his seat in Rochester and Strood, east of London.
Another by-election is also taking place on Thursday, in Heywood and Middleton in Manchester, sparked by the death of Jim Dobbin, the local opposition Labour MP.
UKIP is expected to make major gains in that vote although polls indicate Labour will hold on to the seat.
The party has said it wants to take on both the parties and aims for a kingmaker role in case neither party wins a majority in the general election.