This list notes the number of by-elections by session since 1945-46 together with a list of the the successful candidates in by-elections since 2005.
Two years’ worth of local elections in England are about to be held on the same day, while in Wales 16-17-year olds will be able to vote in elections to the Senedd Cymru for the first time.
These elections will take place alongside those for mayors and police and crime commissioners, as well as a parliamentary by-election, and for the Scottish Parliament on Thursday (6 May).
Some of these were postponed from last May because of the coronavirus and some were already scheduled for May 2021. In England, many hundreds of councillor by-elections, which would normally have happened during the past year, have been held over until 6 May.
This Insight looks at what elections are taking place, the numbers eligible to vote and the percentage of people with up to four elections in their area.
What and where are elections taking place?
The elections for mayors and councillors on local authorities in England coincide with those for police and crime commissioners in England and Wales, and the Greater London Authority and the London Mayor.
Votes are also taking place for the Scottish Parliament and Senedd Cymru. In addition, there is a parliamentary by-election in Hartlepool.
All 48 million people eligible to vote in Great Britain will have the opportunity to cast a vote in at least one election, with voters in some areas having ballots in up to four different elections. Sixteen- and 17-year-olds will be eligible to vote, for the first time, in elections to the Senedd Cymru. The voting age for Scottish Parliament elections has been 16 since 2015.
Three-quarters of voters in Great Britain will be able to vote in more than one election
Many people will have more than one election taking place in their area. As the chart below shows, more than half of eligible voters (57%) will be able to vote in two, followed by 18% in three elections and 2% in four.
Voters in Liverpool, Bristol, Cambridge and Hartlepool will have four elections. They will all vote for district or borough councillors, and police and crime commissioners. In Liverpool and Bristol, two mayoral elections will also take place, and in Hartlepool there will be an election for a mayor and a parliamentary by-election. In Cambridge there will also be an election for a mayor and county council councillors.
% of electorate by number of elections on 6 May 2021
Voters in the elections for the London Assembly, Scottish Parliament and Senedd Cymru have two votes: one for an individual candidate and one for party or independent “top up” member.
Furthermore, the by-elections in councils that could not be held because of the pandemic, as well as for parish councils in some parts of England, will add to the number of ballots in those areas.
When will we know the results?
Some results could be known overnight on Thursday, like the Hartlepool by-election. But the combination of making the process Covid-secure, and the number of votes that will have to be counted, could mean that the results will take longer than usual.
In Scotland the count is not being done overnight and the results are expected to start with the first-past-the-post (FPTP) seats on Friday with the regional top-up seats being finalised during and Saturday, possibly the last around 7pm.
In Wales, the first Senedd results are expected from around 3pm on Friday with the top-up regional results later in the evening after 7pm. In London, results for FPTP seats might start to be declared on Friday evening and the remainder on Saturday. The results of the London mayor election may come late on Saturday but could be on Sunday.
There is no fixed timetable for the other results but only a few authorities are planning to count on Thursday night. Most of the councils are understood to be counting during the day on the Friday, with most results expected in the afternoon and evening. Some authorities, however, are not starting to count until Saturday. The results for Police and Crime Commissioners might not be known until Monday.
The Library will publish a series of briefings on the results of the May 6 elections. You can sign up for up for research alerts on our website.
Note: The number of registered electors used in this analysis is based on data for March 2020 for England and Wales from the Office for National Statistics; and Electoral Statistics for Scotland for December 2020.
For further details of these elections see Coronavirus: Elections, House of Commons Library, 14 April 21.
About the author: Richard Cracknell is Head of the Social and General Statistics section at the House of Commons Library.
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