Additional Member System

The additional member system (AMS) is used for electing the Scottish Parliament, Welsh Assembly and Greater London Assembly. 

Most (about two-thirds) of the seats are elected by first-past-the-post. The rest of the seats are awarded by the regional list system.

Voters have two votes, one for first-past-the-post and the other on the regional list system.

The list system operates where each party offers a list of candidates for that region. Voters chose a party rather than an individual. Seats are awarded in proportion to the votes cast for each party in each region.

The Additional Member System (AMS) is used in the UK for elections to the Scottish Parliament, the Welsh Assembly and the Greater London Assembly. It is intended to mix aspects of FPTP and proportional representation – it is neither wholly proportional nor wholly majoritarian. Its proponents claim it forms a hybrid of the two types of system that combines their advantages and avoids their disadvantages.   

The seats awarded on the list system are not in proportion to votes cast, but are distorted in favour of those parties that have been most disadvantaged in the  constituency, first-past-the-post system. This is called the differential top-up system. 


Before 2011, the system produced either minority or coalition governments because no party won an overall majority. However, in 2011 the Scottish National Party did win an overall majority in the Scottish Parliament, and Labour won exactly half the seats in Wales. We can now say that its impact on the main parties is unpredictable.

How does it work?

·      Voters have two votes: the first is for a constituency representative, who is elected using FPTP; the second is for a party list and uses multi-member regional constituencies, introducing an element of proportional representation.

·      There are fewer list members than constituency representatives, and so they are known as 'additional' or 'top up' members. In the Scottish Parliament, 73 of the 129 members are elected in single-member constituencies, with the remaining 56 seats being filled by list members. In the Welsh Assembly 40 of the 60 members represent single-member constituencies, with 20 list members. In the GLA 14 of the 25 members are elected in single-member constituencies and 11 are top-up members.

·      These bodies have four-year fixed terms.

·      The top up component introduces a proportional element, acting as a corrective to the FPTP part of the system. A calculation is made using the D'Hondt formula (explained above) to determine how many members a party should be allocated from the lists. For example in Scotland the Conservative Party won no seats in the 1997 Westminster election under FPTP, but the list enabled it to win a total of 18 seats in the first Scottish Parliament elections in 1999.

·      The FPTP element maintains a strong link between the member and the constituency.

·      Electors have wider choice than under straight FPTP; they can vote for a 'split ticket' if they wish, using their constituency vote to choose a representative from one party, and their top-up vote to support another party.

AMS has produced stable coalitions in Scotland and Wales which have been able to agree and make significantpolicy decisons- so this suggests that AMS is just as good as FPTP at producing 'strong and stable' government.


In 2023, the Welsh Parliament reform bill committee recommended reforms included taking the 32 new constituencies that will be used in the next general election and pairing them to create 16 Senedd constituencies – with each returning six members in multi-member districts. Opposition to the proposed closed-list voting system was expressed by some Labour and Plaid Cymru representatives, while opposition to the overall expansion of the Senedd was expressed by some Labour representatives  and the Conservatives