The Additional Member System allows for single member constituencies decided on a majoritarian basis but is has a proportional element and so is a mixed system.
Voters cast their votes in two ways.
They vote for an MP who is elected by First Past the Post for their constituency but they have another vote for a party and this is used to elect additional MPs on a proportional basis.
The top up can be used to make the final result more or less proportionate as in the German system or it can be extra so that it adds a proportional element but does not correspond with the proportion of votes across the country as a whole as in Scotland and Wales.
