Senedd reform: a glossary

Published 06/06/2022   |   Reading Time minutes

Since 2004, a series of reports have recommended that the size of the Senedd should increase from its current 60 Members. Our article Senedd Reform- the story so far sets out some of this history.

The Special Purpose Committee on Senedd Reform was set up in October 2021 to come up with proposals to be included in a Welsh Government Bill to reform the Senedd. This article provides an explanation of some of key terms used in that Committee’s report, Reforming our Senedd. Our article on Reforming our Senedd summarises its key findings and the next steps for Senedd Reform.

The report will be debated by the Senedd on 8 June.

Key terms

Boundary review

The boundaries for UK election constituencies are usually reviewed periodically to make sure they reflect factors such as population changes. The Committee recommends a streamlined boundary review for the 2026 election, a full boundary review before the 2031 election and reviews periodically after that. It says a Senedd Reform Bill should set out the parameters for future reviews and that responsibility for reviews should sit with the Local Democracy and Boundary Commission for Wales.

Closed list proportional representation

A form of electoral system where each party puts forward a list of their candidates for multi-member constituencies. Winning candidates are taken from the lists in order of their position, and seats are allocated proportionally using a formula. In a closed list system, parties put forward a fixed list in an order of their choosing. Voters don’t have a say in how the list is organised, and the voter simply votes for a party’s list. This is the system recommended by the Committee. It’s also the system currently used for regional seats in the Senedd.

Committee on Senedd Electoral Reform (CSER)

CSER was established in September 2019 to consider the findings of the Expert Panel on Electoral Reform. It was made up of Senedd Members from Plaid Cymru, Labour and the Brexit Party (formerly UKIP). The Brexit Party member resigned before CSER published its findings. It published its final report in September 2020.


Co-terminosity is the sharing of boundaries by constituencies for different elections. For example if the UK Parliamentary boundaries and Senedd boundaries were the same they would be co-terminous. Co-terminosity is said to be helpful in terms of familiarity for voters and parties. Senedd boundaries used to be co-terminous with Westminster boundaries until 2011 when the link was severed. The Committee has suggested that while having some co-terminosity initially will have benefits, this link shouldn’t be kept long term so that Senedd boundaries aren’t affected by changes to Westminster constituencies which the Senedd has no control over.

D’Hondt method

A formula used to turn votes into seats in a proportional electoral system. The formula is already used for regional seats in the current Senedd. The number of votes cast for each party is divided by the number of seats the party has already won, plus one. For example, if a party has won two seats, the number of votes won is divided by three. The party with the highest number of votes each round wins the seat, and this is repeated until all seats have been filled. This is the method recommended by the Committee.

District magnitude

District magnitude is the number of members returned by each constituency. The Special Purpose Committee has recommended that six members should be elected in 16 constituencies in Senedd elections in future. This would mean a district magnitude of six. The higher the district magnitude or number of members representing an area the more proportional the results are likely to be. District magnitudes that are too high can risk being ‘hyperproportional’ allowing a parties or candidates with very low levels of overall support to win seats.

Expert Panel on Assembly Electoral Reform

The Expert Panel was established in February 2017 to provide politically impartial advice to the Llywydd and the then Assembly Commission on the number of Members the Senedd should have, the most suitable electoral system to use and other related matters. It consisted of six academics, and was chaired by Professor Laura McAllister. It published its report in November 2017.

Gender quotas

Gender quotas in the context of elections, are rules which demand that a certain number or percentage of a certain gender be represented in the pool of candidates that are up for election. The Committee recommends that the Senedd should be elected with integrated statutory gender quotas.

Multi-member constituencies

Multi-member constituencies are constituencies which return more than one member. The regional lists used to date in Senedd elections are one example. The Committee proposes in future that each constituency in Senedd elections would elect a total of six members. This is different to ‘first-past-the-post’ electoral systems like the one used to elect UK MPs where just one member is elected to represent a constituency.


The Committee has recommended that 16 new Senedd constituencies should be created. It says they should be based on the pairing of the 32 new UK Parliament constituencies that will be in place by 2023. Pairing means matching together two different constituencies to make one new one. The Committee says a ‘streamlined’ boundary review should be carried out to pair constituencies before 2026.

Sainte-Laguë method

A formula used to turn votes into seats in a proportional electoral system. It’s similar to the D’Hondt method, the main difference being the divider used in each round. In the Sainte-Laguë method the number of votes is divided by twice the number of seats won, plus one. For example after a single seat has been won, the next round uses the divider three, as this is double one (the seat won in the first round), plus one. This leads to dividers of one, three, five, seven and so on for each round, until all seats have been allocated. This method wasn’t recommended by the Committee, although a minority did argue in its favour.

Single Transferable Vote (STV)

A proportional electoral system where voters number candidates in order of preference in multi-member constituencies. Each voter has one vote. If a voter’s first choice has enough votes to win a seat, or if their first choice has no clear chance of winning, the voter’s second choice will be given their vote. Any votes in excess of the quota for the winning candidate will move to the voter’s second choice. This continues until every seat in the constituency is filled. This was the system recommended by the Expert Panel and CSER, but not by the Committee. A minority on the Committee favoured this method.


The Government of Wales Act 2006 says that Bills related to the membership of the Senedd, its constituencies and the systems by which Members are returned must be passed by a supermajority of Senedd Members rather than a simple majority as with other Bills. This means that Bills on these subjects need 40 Members of the Senedd to vote for them at the final stage of the Bill process in order for them to pass. This is set out in detail in Section 111A of the Government of Wales Act 2006. In several places, the report make reference to the fact that the majority of Committee in favour of a recommendation represents a legislative supermajority within the Senedd.


A procedure where a party’s list of candidates alternates between male and female candidates. This ensures that equal numbers of male and female candidates appear on party lists. This is already used by some parties in Senedd regional elections. It is recommended by the Committee for use in a reformed Senedd.

Article by Rhun Davies, Philip Lewis & Nia Moss Senedd Research, Welsh Parliament