Mixed-member majoritarian (MMM) systems are used in a number of countries, including several countries in Eastern Europe (for example, Hungary, Russia and Lithuania). Superficially, these systems resemble the highly proportional Additional Member systems (AMS) used in Germany and New Zealand - under both systems, voters choose a local constituency representative (usually under FPTP), and regional representatives under a proportional system.
However, whereas in AMS the regional seats are allocated in a way that compensates for the disproportionality of the FPTP constituency election, in MMM the regional seats are allocated in addition to the FPTP constituency seats. This means that the regional seats compensate only very marginally for the disproportionality in the FPTP section.
Because of this, we believe that MMM has only a minimal advantage over FPTP. If the UK is going to the trouble of changing our voting system, we can surely do better than MMM.
The only reason we include MMM in our list of voting systems is to make clear the distinction between MMM (which is a terrible voting system) and AMS (which has much to recommend it).
