Senedd By-Elections: A History of Welsh Parliament Special Polls
The Senedd (Welsh Parliament, or Senedd Cymru), formerly known as the National Assembly for Wales, occasionally holds by-elections to fill vacancies that arise between general election cycles. These special polls are critical moments in Welsh politics, often reflecting shifts in public sentiment or the resilience of a political party's stronghold.
By-elections occur when a Member of the Senedd (MS) vacates their seat due to resignation or death. While some seats remain with the incumbent party, others see a change in political representation, altering the balance of power within the parliament.
Key Facts
- By-elections in the Senedd are triggered by the death or resignation of a sitting member.
- Political parties such as Labour and Plaid Cymru have historically contested these seats.
- The most recent recorded by-election occurred in Caerphilly on October 23, 2025.
- Some by-elections have resulted in gains for Independent candidates, as seen in the Blaenau Gwent contest.
Analysis of Senedd By-Election Results
Over the various assembly terms since the Senedd's inception, several by-elections have taken place. These events range from straightforward party retentions to surprising political shifts.
Recent and Notable Shifts
In the 2021–2026 term, the Caerphilly by-election on October 23, 2025, saw a significant change. Following the death of Labour's Hefin David, the seat was won by Lindsay Whittle of Plaid Cymru.
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Historical Continuity and Changes
Other by-elections have seen parties successfully defend their seats. For example, in the 2016–2021 term, Jack Sargeant retained the Alyn and Deeside seat for Labour following the death of Carl Sargeant. Similarly, Rhun ap Iorwerth maintained Plaid Cymru's hold on Ynys Môn in 2013 after Ieuan Wyn Jones resigned to lead the Menai Science Park.
A unique case occurred in the 2003–2007 term in Blaenau Gwent. Peter Law had left the Labour Party to sit as an independent before his death. The subsequent by-election on June 29, 2006, was won by his widow, Trish Law, who ran as an Independent, marking a gain from Labour.
Summary of Senedd By-Elections
| Term | Constituency | Date | Winner | Party | Cause |
|---|---|---|---|---|---|
| 2021–2026 | Caerphilly | 23 Oct 2025 | Lindsay Whittle | Plaid Cymru | Death |
| 2016–2021 | Alyn and Deeside | 6 Feb 2018 | Jack Sargeant | Labour | Death |
| 2011–2016 | Ynys Môn | 1 Aug 2013 | Rhun ap Iorwerth | Plaid Cymru | Resignation |
| 2003–2007 | Blaenau Gwent | 29 Jun 2006 | Trish Law | Independent | Death |
| 1999–2003 | Swansea East | 27 Sep 2001 | Valerie Lloyd | Labour | Death |
Frequently Asked Questions
What is the Senedd?
The Senedd, or Senedd Cymru, is the Welsh Parliament, previously known as the National Assembly for Wales.
Why are by-elections held in the Senedd?
By-elections are held to fill a vacancy in the parliament when a member dies or resigns from their position.
Has a seat ever changed parties during a Senedd by-election?
Yes. For instance, the Caerphilly seat shifted from Labour to Plaid Cymru in 2025, and Blaenau Gwent shifted from Labour to an Independent candidate in 2006.
Who won the Ynys Môn by-election in 2013?
Rhun ap Iorwerth won the Ynys Môn by-election, retaining the seat for Plaid Cymru.
What caused the by-election in Alyn and Deeside in 2018?
The by-election was triggered by the death of the incumbent member, Carl Sargeant.