[1][2][3][4] The by-election was triggered by the Conservative MP for Clacton, Douglas Carswell, defecting to the UK Independence Party (UKIP) and subsequently resigning his seat to seek re-election as its candidate.

According to John Curtice, professor of politics at Strathclyde University, the result was the biggest increase in the share of a vote for any party in any by-election in history.

[6] On 28 August 2014, Douglas Carswell, a Eurosceptic Conservative backbencher, announced his defection to UKIP and said that he was resigning his seat in order to fight a by-election.

[10] The poll was one of two parliamentary by-elections the same day, with an election also being held in the constituency of Heywood and Middleton following the death of its MP, Jim Dobbin of the Labour Party.

[15] Evans also suggested, however, that the Conservatives should consider not standing in the by-election, which he called "a total distraction",[16] while the backbencher Zac Goldsmith described Carswell as a "model Parliamentarian" and remarked that "I have nothing but admiration for him".

[20] During the campaign, on 27 September 2014, a second Conservative MP and close friend of Carswell's, Mark Reckless, likewise defected to UKIP and sought re-election in a by-election for his constituency of Rochester and Strood in Kent.

On 29 August 2014, The Daily Telegraph journalist Peter Oborne wrote: "David Cameron should go down on his knees and beg Boris Johnson to stand as the Conservative Party's candidate for Clacton in the coming by-election.

"[26] Two Conservative MPs, Matthew Offord and John Stevenson, wrote a joint article calling for Johnson to stand in the by-election.

[29] The Conservative candidate was the actor and Tendring District councillor Giles Watling who was chosen by an open primary, in which 240 local residents voted, on 11 September.

[34] The Liberal Democrat candidate, Andy Graham, is the former mayor of Bishop's Stortford in Hertfordshire,[35] as well as an actor and author of children's books.

[42] Sizer was a consultant oncologist at Colchester Hospital who stood as a single-issue candidate to get health and cancer care onto the agenda of the political parties.

[52][53][54] Both the Prime Minister David Cameron[55] and the Labour leader Ed Miliband[56] visited the constituency to help their respective party campaigns.

Ten days before the election, the artist Banksy painted a mural on a wall in Clacton which showed five grey pigeons holding three placards.

[57] Two days before the election, Boris Johnson was unable to remember the name of the Conservative candidate in the by-election during an interview with Nick Ferrari, saying "he's a superb man.