UK By-Elections Explained
A Parliamentary by-election chooses a new MP for one constituency between general elections. The rules are familiar, but the political circumstances can be very different: attention and campaign resources are concentrated on one seat, turnout can be unpredictable and voters may use the contest to send a message to the government or the main parties.
Use these explainers to understand the real politics of by-elections, then put those ideas into practice in Political Earthquake.
About the simulation
Start with the basics
What is a UK Parliamentary by-election?
A by-election fills one vacant Commons seat between general elections. Understand why vacancies happen, how a writ is issued and how FPTP works in a single constituency.
By-elections explained →Why are by-elections different from general elections?
Same voting system, different political context. Explore how concentrated resources, media attention and voter motivation make by-elections distinctive.
Differences explained →Why can turnout be lower in a by-election?
Fewer voters may participate when the government is not being chosen — but turnout can also surge when the contest is close or controversial.
Turnout explained →Campaigning and voter behaviour
What is tactical voting in a by-election?
Under FPTP, voters may back a second-choice candidate to influence the result. By-elections can intensify this behaviour.
Tactical voting explained →How important are candidates in by-elections?
Candidate quality, local connections and media performance can matter more when one seat gets national attention.
Candidates explained →Why can smaller parties perform well in by-elections?
Concentrated resources, protest voting and local credibility can help parties with few MPs outperform their national position.
Smaller parties explained →Political consequences
Why do governing parties often lose by-elections?
Mid-term unpopularity, protest voting and opposition coordination create a pattern — but not a rule.
Government losses explained →How can a by-election change the political narrative?
One constituency result can affect leadership pressure, media coverage, morale and expectations about future contests.
Narratives explained →Which by-elections have changed British politics?
From Orpington 1962 to Tiverton and Honiton 2022 — landmark results and what each reveals about voters and parties.
Case studies →