East Midlands

Derbyshire

1: Richard Bell defected from Labour to the Liberal Party in 1904, leaving the Liberals with seven seats and Labour with none.
2: John Hancock ( Mid Derbyshire) defected from the Liberal Party to Labour in 1909, leaving the Liberals with six seats and Labour with one.
3: Henry Petty-Fitzmaurice defected from the Liberal Unionist Party to the Conservative Party in 1912, leaving the Conservatives with two seats and the Liberal Unionists with none.
4: The 1913 Chesterfield by-election was won by Barnet Kenyon ( Liberal-Labour), gaining the seat from Labour. This left Labour with three seats and Liberal-Labour with one.
5: WE Harvey ( North East Derbyshire) defected from Labour to the Liberal Party in March 1914, leaving the Liberals as the largest party with four seats, and Labour with two.
6: The May 1914 North East Derbyshire by-election was won by Harland Bowden ( Conservative), gaining the seat from the Liberal Party. This left the Liberals and Conservatives as the joint largest parties with three seats each.
7: John Hancock defected from Labour to Liberal-Labour in 1915, leaving Liberal-Labour with two seats and Labour with one.
8: JH Thomas defected from Labour to National Labour in August 1931, leaving Labour with seven seats and National Labour with one.
9: The 1936 Derby by-election was won by Philip Noel-Baker ( Labour), gaining the seat from National Labour. This left Labour with five seats and National Labour with none.
10: The 1944 West Derbyshire by-election was won by Charles Frederick White ( Independent Labour), gaining the seat from the Conservative Party. This left Labour as the largest party with five seats, the Conservatives with four, and Independent Labour with one.
11: Chris Williamson ( Derby North) was suspended from the Labour Party between February and June 2019, and again from September 2019. During his suspensions, this left Labour with four seats, and Williamson as the sole indepedent.

Leicestershire and Rutland

1: The 1891 Harborough by-election was won by Paddy Logan ( Liberal), gaining the seat from the Conservative Party. This left the Liberals as the largest party with four seats, and the Conservatives with three.
2: The 1894 Leicester by-election was won by Henry Broadhurst ( Liberal-Labour) and Walter Hazell ( Liberal), gaining one of the seats from the Liberals. This left the Liberals with four seats and Liberal-Labour with one.
3: The March 1906 Leicester by-election was won by Franklin Thomasson ( Liberal), gaining the seat from Liberal-Labour. This left the Liberals with five seats, and Liberal-Labour with none.
4: The March 1922 Leicester East by-election was won by George Banton ( Labour), gaining the seat from Coalition Liberal. This left Labour and the Coalition Liberals with one seat each.
5: The 1927 Bosworth by-election was won by William Edge ( Liberal), gaining the seat from the Conservative Party. This left the Conservatives with five seats and the Liberals with one.
6: The 1967 Leicester South West by-election was won by Tom Boardman ( Conservative), gaining the seat from Labour. This left Labour and the Conservatives with four seats each.
7: Tom Bradley defected from Labour to the Social Democratic Party in 1981, leaving Labour with two seats and the SDP with one.
8: The 2004 Leicester South by-election was won by Parmjit Singh Gill ( Liberal Democrats), gaining the seat from Labour. This left Labour with four seats and the Liberal Democrats with one.
9: Claudia Webbe ( Leicester East) was suspended from the Labour Party in 2020, and ultimately expelled in 2021, leaving Labour with two seats and Webbe as the sole independent.
10: Andrew Bridgen had the Conservative whip withdrawn in January 2023, and was ultimately expelled from the party in April 2023, leaving the Conservatives with six seats and Bridgen as one of two independents. He joined the Reclaim Party in May 2023, becoming their sole MP. He resigned from Reclaim in December 2023, subsequently once again sitting as an independent.

Lincolnshire

1: Edward Heneage ( Great Grimsby), Henry Meysey-Thompson ( Brigg) and Joseph Ruston ( Lincoln) all defected from the Liberal Party to the Liberal Unionist Party in June 1886, leaving the Liberals with four seats and the Liberal Unionists with three.
2: The 1887 Spalding by-election was won by Halley Stewart ( Liberal), gaining the seat from the Conservative Party. This left the Conservatives with eight seats and the Liberals with two.
3: The 1893 Great Grimsby by-election was won by Edward Heneage ( Liberal Unionist), gaining the seat from the Liberal Party. This left the Liberals with six seats and the Liberal Unionists with one.
4: The 1894 Brigg by-election was won by John Maunsell Richardson ( Conservative), gaining the seat from the Liberal Party. This left the Liberals and Conservatives with five seats each.
5: George Doughty ( Great Grimsby) defected from the Liberal Party to the Liberal Unionist Party in 1898, and resigned his seat, triggering a by-election, which he won. This left the Liberals and Liberal Unionists with three seats each.
6: The 1907 Brigg by-election was won by Berkeley Sheffield ( Conservative), gaining the seat from the Liberal Party. At a similar time, Leslie Renton ( Gainsborough) defected from the Liberals to the Liberal Unionist Party. This left the Liberals with six seats, the Conservatives with three, and the Liberal Unionists with two.
7: George Doughty defected from the Liberal Unionist Party to the Conservative Party in 1912, leaving the Conservatives with five seats and the Liberal Unionists with none.
8: The 1920 Louth by-election was won by Thomas Wintringham ( Liberal), gaining the seat from the Conservative Party. This left the Conservatives with seven seats and the Liberals with one.
9: The July 1924 Holland with Boston by-election was won by Arthur Dean ( Conservative), gaining the seat from Labour. This left the Conservatives with six seats and Labour with none.
10: The March 1929 Holland with Boston by-election was won by James Blindell ( Liberal), gaining the seat from the Conservative Party. This left the Conservatives with seven seats and the Liberals with one.
11: The 1942 Grantham by-election was won by Denis Kendall ( Independent), gaining the seat from the Conservative Party. This left the Conservatives with six seats and Kendall as the sole independent.
12: Dick Taverne ( Lincoln) defected from Labour to the Democratic Labour Party in 1973, and resigned his seat, triggering a by-election, which he won. This left Labour with two seats and Democratic Labour with one.