Constituency profile: Batley and Spen
The constituency was created in 1983 from parts of the seats of Batley and Morley, Brighouse and Spenborough, and Dewsbury.
It has seen significant boundary changes since its creation – most notably those that took effect for the 1997 general election.
The town of Heckmondwike was part of the seat from its creation in 1983 until 1997, when it was transferred to Dewsbury. Heckmondwike was returned to Batley and Spen for the 2010 general election.
Currently, the Batley and Spen constituency covers the Kirklees Council wards of Batley East, Batley West, Birstall and Birkenshaw, Cleckheaton, Heckmondwike, and Liversedge and Gomersal.
Traditionally Batley and Heckmondwike have been inclined to vote Labour, while the other settlements have been more inclined to vote Conservative. The exception is Cleckheaton, which has returned Liberal Democrat members for the local council.
The seat swung in Labour's favour in the elections of 1997, 2001 and 2005, but the Conservatives reduced the Labour majority in 2010 with a swing below the national average.
Jo Cox was elected for Labour in 2015. Following her murder in 2016, a by-election was held, which was won by Tracy Brabin who retained the seat for Labour with a large majority of 16,537.
The Conservative Party, Liberal Democrats, UK Independence Party and the Green Party all announced they would not contest the 2016 by-election as a mark of respect for Mrs Cox.
Ms Brabin's majority was almost halved at the 2017 general election, when she won by 8,961 votes.
A second by-election in five years will be held in Batley and Spen in the coming weeks, following Ms Brabin's victory in the West Yorkshire mayoral poll on Sunday.
Several bookmakers have already made the Conservatives the favourites to win the seat for the first time since 1997.