By-Elections (for the party in power)

Today (20/07/2023) sees three by-elections in the UK taking place; by the time you're reading this, the results may have already come in, so the blogpost may be out of date. However, two interesting questions are:

• How often do by-elections happen, and
• What results does the ruling party experience in a by-election?

For the purposes of simplicity, the data in this blogpost dates back to 1945. Since then, there have been twenty-one general elections, resulting in:

• Eight Labour majorities (1945, 1950, 1964, 1966, 1974 (Oct), 1997, 2001, 2005)
• One Labour minority (1974 - Feb)
• Ten Conservative majorities (1951, 1955, 1959, 1970, 1979, 1983, 1987, 1992, 2015, 2019)
• One Conservative minority (2017)
• One coalition government consisting of the Conservatives and Lib Dems (2010)

There have been 517 (according to this report) by-elections since that point in time. And here is some data about those elections by time period between general elections:

From 1945-55, the party in power kept hold of all their seats, with the 1997-2001 Labour government of Tony Blair being more successful by gaining a seat - the only time a party has come out of a set of by-elections with an increase in seats. In total, 270 seats (up to today) have seen the party in power face a by-election; 193 times, that seat has been held by the party (a 71.5% success rate), whilst seven seats have also been gained in total from other by-elections. From 1987-1997, meanwhile, the Conservatives held 18 seats before by-elections, yet lost 15 of them, with all eight seats from 1992-97 lost.

In fairness, seven is quite a low number over the course of seventy-five years, indeed it only happened in the governments of Harold MacMillan, Margaret Thatcher, Tony Blair, David Cameron and Boris Johnson. Under Blair, that was only due to those seats being held before by the Speaker (who both happened to be representing Labour anyways).

But who's gaining those 77 lost seats then? Cue a graph: 

I've included the Lib Dems (formerly the Liberal Party) as they seem to be one of the main contenders for many by-elections recently. Technically, a few of the "other" seats were taken by the SDP, which merged with the Liberal Party to form the Lib Dems, but I've not included them in that data. Many parties, such as UKIP, the SNP and Plaid Cymru are part of that "other section".

Obviously, graphs can be misleading - this second one is by percentage, so no, the Lib Dems didn't rout the Tories when Theresa May was in government, and so I'll include some final tables here: