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.


  • There are two types of representative — those elected in constituencies and those elected by the list system,

  • The system increases voter choice, as voters have two votes.

  • It enables smaller parties, such as the Greens, to win some seats.

  • The overall outcome tends to be approximately proportional to support for all parties.

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.


  • · It creates two different types of member: some with constituency responsibilities and some without. However, there is little evidence that the second category is seen as having less legitimacy.

  • A closed list system is used, which means that the party leadership ranks candidates in order on the list. It can use this power to limit the chances of dissident members of the party being elected.

  • · Smaller parties achieve less representation than under a fully proportional system. This is especially true in Wales where the small number of top-up seats has advantaged Labour -(However, In London in 2016, there were twelve parties on the party list, ranging from the Animal Welfare Party to the Women's Equality Party. Alphabetically in Scotland in 2007, two regions had 23 parties to choose from.)

  • . The SNP has been the dominant party in Scotland since 2007, running a majority government in 2011-16. However the SNP are now 2022- in coalition with the Green Party. AMS may have contributed to the rise of Nationalism in Scotland

  • Coalitions are more likely- and you could argue that coalitions formed after an election have no mandate- since no-one voted for a coalition.