Phillips had won a large majority of 39% in 2015, and the Labour Party candidate came second. The constituency had been held by the Conservatives since it was first contested in the 1997 general election and was considered a safe seat for the party. Sleaford and North Hykeham is estimated to have had a vote-share of more than 60% in favour of leaving the EU in the June 2016 EU membership referendum and Brexit was a key issue in the by-election campaign. Phillips had supported a UK withdrawal from the EU but resigned in opposition to the government's handling of the issue – he felt Parliament was not being consulted sufficiently.