The Conservatives nominated Caroline Johnson, a paediatrician, to replace Phillips; she won the by-election with more than 50 per cent of the vote, a sizable majority.

Phillips had supported a UK withdrawal from the EU but resigned in opposition to the government's handling of the issue – he felt that Parliament was not being consulted sufficiently.

The UK Parliament constituency of Sleaford and North Hykeham is located in Lincolnshire, which is in the East Midlands region of England.

[22][16] Due to the first-past-the-post electoral system used in British general elections, UKIP won fewer seats than the Liberal Democrats despite winning a higher vote share nationally.

The researcher Chris Hanretty published estimates of the referendum results from each constituency, and calculated that voters in Sleaford and North Hykeham voted 61.6 per cent in favour of leaving the EU.

[31][32] On 3 November 2016, the High Court had ruled the UK could not invoke Article 50 to begin the process of leaving the EU without a parliamentary vote.

[33][34] The day after the High Court ruling, Phillips resigned his parliamentary seat over the issue, citing policy differences and criticising the Conservative government under May for failing to consult Parliament sufficiently over Brexit.

[36] In his resignation letter to his local Conservative Association, Phillips said; "The referendum result gives the government no authority or mandate to adopt a negotiating position without reference to the wishes of the House and those of the British people expressed through their elected representatives".

[10] The Daily Telegraph reported that some Conservative MPs said that Phillips, who is a lawyer, may have been motivated by disappointment over not being promoted to Attorney General.

[39] It came less than two weeks after the Conservative MP Zac Goldsmith resigned in protest against the government's decision to support the expansion of Heathrow Airport.

[49] After her selection, Johnson said; "I am completely behind the Government's plans for Brexit and to deliver on the decision made by the British people".

[48][58] The Liberal Democrats selected Ross Pepper, who worked for an optician, on 11 November;[59] he had stood in Lincoln in the 2015 general election, coming third.

[77] On 5 December, Farage campaigned in front of a poster on which "Hykeham" was misspelt as "Hykenham", which The Guardian speculated could hurt his party's chances in the election.

[80] The Conservatives were expected by journalists to win the Sleaford and North Hykeham by-election;[9][10][77] in an opinion piece in The Guardian on 4 December, the journalist Andrew Rawnsley argued that whether UKIP would overtake Labour was the most important question in the by-election, and speculated whether this could indicate a realignment of British politics based on views on Brexit instead of the traditional left–right political spectrum.

Only the Lib Dem candidate is concentrating on the 40% of voters in the constituency who backed remain last June.The election took place on 8 December 2016.

[68][86][87][88][90] The leadership of Jeremy Corbyn was also cited as a reason for the poor performance, including by Jess Phillips – the Labour MP for Birmingham Yardley.

[68][88] David Winnick, the Labour MP for Walsall North, called the result "humiliating" and said it could foreshadow an "electoral disaster" for the party.

[68] Vernon Coaker, Labour MP for Gedling, said that the result was disappointing, and blamed the focus on Brexit instead of on issues like the NHS.

[68] UKIP's performance was also seen in some quarters as poor, even though they beat both Labour and the Liberal Democrats, as their vote-share declined in comparison with the 2015 general election results.

[68][87] Johnson retained her seat at the 2017 general election, winning a large majority of more than 25,000 votes over the Labour Party candidate, who came second.