Alternative vote top-up

The Alternative Vote Plus (AV ) or Alternative Vote Top-up is a voting system intended for use in elections to an assembly or legislature. Under AV most candidates are elected from single member constituencies under the Alternative Vote system while a small number of candidates are elected under the regional list system. AV is not a parallel voting system. Rather, as occurs under the Additional Member System (AMS), under AV seats filled from regional lists are so allocated as to off-set the disproportionality created by the single seat constituencies and to achieve a measure of proportional representation.

AV may be considered a variant of AMS. However, unlike most versions of AMS, AV is not designed to deliver a high level of proportional representation. Rather, under AV the number of candidates elected from regional lists is kept to a relatively small "top up" in order to grant an in-built electoral advantage to larger parties. AV also differs from most versions of AMS in that the constituency seats are elected by means of the Alternative Vote rather than the Simple Plurality ('First past the post') system.

AV was invented by the 1998 Jenkins Commission, which recommended it as a system for use in United Kingdom general elections, but no action has yet been taken on that committee's recommendations. The Commission described the system as a "limited" form of AMS aimed at achieving a balance between the requirements of "broad proportionality" and "stable government".