Electoral systems revision: AMS in action

That the London Assembly is elected using the Additional Member System is little known or much misunderstood

Yesterday’s vote for the Mayor of London took place alongside the vote to elect the Greater London Authority’s Assembly. These 25 London Assembly Members are expected to check and scrutinise the Mayor’s actions. Unfortunately it is hamstrung by having relatively little power and also the fact that so few people know it exists.

But the task here is to focus on up-to-date examples of how AMS is used with half an eye on the AS examinations.

The Assembly consists of 35 members, with 14 elected to represent different areas across London and 11 representing London as a whole.

The 14 Constituency Assembly Members are elected using first-past-the-post and like Westminster contests the candidate with the largest number of votes wins.

The London-wide Assembly members contest seats by party (unless independent). It is here that things get a bit complicated. Seats are allocated according to a version of the d’Hondt formula – similar to that used in elections conducted under the Single Transferable Vote. This takes into account the number of seats won in the Constituency contests and the percentage of vote cast on the London-wide ballot. Further, it is also necessary to exceed a 5% threshold – in 2004 both Respect and the BNP failed by a margin of under half of one per cent here.

The calculation is: total number of votes won/seats already won (including Constituency seats) +1

So after each round the party with the highest number takes the London-wide seat.

In short, the calculation works to “top-up” those parties that have won a percentage of the vote that is proportionately higher than the seats won to seats available after taking into account the Constituency outcome. It generally favours parties whose vote was not sufficiently concentrated as to pick up seats.

In 2004 the Conservatives won 9 of 14 Constituency seats and so won no additional London-wide seats. By contrast the Liberal Democrats won no Constituency seats and picked up 5 London-wide seats.

It is widely predicted that both BNP and Respect will have won a large enough share of the votes to pick up seats in the Assembly in the London-wide contest. For better or worse, at least it will raise the profile of this part of the elected Authority.

We will update once the 2008 results come in.

Background information from the London elects website
Factsheet 12: How the London Assembly is elected

Factsheet 8: Results from the 2004 London elections