Causes of Byelections since the ‘Reform Act’

CauseNumber of Byelections


Death1,239
Resignation (voluntary appointment to an office of profit under the crown of an MP who wished to vacate a seat)1,064
Appointment to Ministerial Office (1)677
Succession to the Peerage235
Elevation to the Peerage217
Elections declared void on Petition193
Members seeking re-election (voluntary appointment to an office of profit under the crown of an MP who wished to vacate a seat in order to seek a vote of confidence from their constituents)51
Acceptance of office which necessitated re-election36
Members elected for more than one seat declining those they did not wish to represent26
Disqualification from membership of the House of Commons (2)16
Expulsion from the House of Commons8
Members declared bankrupt (3)3
Creation of a new seat during a Parliament2
Seat vacant for Members having voted before taking the oath (4)2
Member certified as insane (5)1


TOTAL3,770

This analysis does not include vacancies for which no byelections were held because of a dissolution of parliament. Much of the research work on which this table is based was undertaken by the late F.W.S. Craig.

Most causes of byelections are matters of common law. The notes list those which derive from statute law.

  1. Under the Succession to the Crown Act 1707. The Re-Election of Ministers Act 1919 severely restricted the necessity to seek re-election on appointment to government office. The Re-Election of Ministers Act (1919) Amendment Act 1926 ended the practice.
  2. A list of offices which are considered ‘Offices of Profit under the Crown’ and thereby disqualify for membership of the House of Commons is contained in Schedule 1 to the House of Commons Disqualification Act 1975, as amended. The Act gives the Secretary of State the power to amend Schedule 1 by Order in Council on resolution of the House of Commons and is in practice continuously changing. This category also includes other disqualifications:
  3. Under the Bankruptcy Act 1883. This category includes two cases of Irish constituencies where the Bankruptcy Act 1883 did not apply and the situation was governed by the Bankruptcy (Ireland) Amendment Act 1872. Therefore in Ireland, bankruptcy vacated the seat but did not disqualify, and one of the Members successfully sought re-election.
  4. Of which, 1 deliberately and 1 inadvertently.
  5. Under the Luncacy (Vacating of Seats) Act 1886. There was at least one case before the passage of this Act of a Member found to be of unsound mind, who could not be deprived of his seat - John Bell, MP for Thirsk in July 1849. The Lunacy (Vacating of Seats) Act 1886 was repealed and replaced by the Mental Health Act 1959 (without the previous provision to fine those disqualified who continue to sit and vote in the House); the Mental Health Act 1959 was itself repealed and replaced by the Mental Health Act 1983.
NB: The 'Reform Act' is the popular title for the Representation of the People Act 1832 (2 & 3 Wm IV, c. 45), the Representation of the People (Scotland) Act 1832 (2 & 3 Wm IV, c. 65), and the Representation of the People (Ireland) Act 1832 (2 & 3 Wm IV, c. 88), with two other related Acts defining constituency boundaries.