Additional Member System

The Additional Member System (AMS) uses a mix of First Past the Post constituencies and Party Lists.

Additional Member System AMS

The Additional Member System is a mix of Westminster’s First Past the Post system and Party Lists.

Voters in the UK use the Additional Member System (AMS) to elect the parliaments of Scotland and Wales, and the London Assembly.

When used in Germany and New Zealand it is called Mixed Member Proportional (MMP).

How to vote

Voters have two ballot papers. On the first is a list of candidates who want to be the local Member of Parliament (MP). In Scotland, they are called Members of the Scottish Parliament (MSP) and in Wales, Members of the Senedd (MS). Like a Westminster election, the voter marks their preferred candidate with a cross.

On the second ballot paper is a list of parties who want seats in parliament. Each party will publish a list of candidates in advance. A vote for a party is a vote to make more of their list of candidates into MPs.

How it’s counted

In Scotland, voters elect 73 MSPs from the Westminster-style first ballot paper and 56 from the second ballot paper.

"The numbers of constituency and list seats can be different for each parliament. But the more first past the post seats, the less proportional AMS will be"

Electoral Reform Society

The Westminster-style ballot papers are counted first. The candidate with the most votes in the constituency wins, even if the majority of people didn’t vote for them.

The second ballot papers are then counted. The people counting look at how many seats a party won on the first ballot paper. They then add ‘additional members’ from the party lists to make parliament match how the country voted on the second ballot paper.

So, if a party has 5 MPs from the constituencies and its fair share is 8 MPs then 3 candidates from its list become MPs. This is either done in regions, as in Scotland or Wales, or countrywide, as in New Zealand.

The goal is to provide a proportional parliament but also keep a single local MP.

Effects and Features

The Additional Member System has become popular as some see it as a compromise solution.

But, as a compromise, it keeps Westminster’s ‘safe seats’ that rarely change hands. But also adds lists of candidates chosen by the political parties. While a massive improvement over Westminster’s system, parties still have a lot of control over who gets elected.

Some also argue that the Additional Member System creates two classes of MPs, and that this can create tension. For instance, constituency MPs receive local casework, whilst the party-list MPs do not.

But the list MPs can provide a second layer of representation should the voter feel their MP does not represent them. They also ensure that every party can potentially win seats in every area. This ensures the government can’t ignore parts of the country.

Play our Additional Member system quiz

How much attention were you paying?