The case for AV

The arguments against

All MPs would have the support of a majority of their voters. Following the 2010 General Election, two thirds of the MPs elected lacked majority support, the highest figure in British political history.

AV is not proportional representation and in certain electoral conditions, such as landslides, can produce a more disproportional result than First Past the Post (FPTP)

It retains the same constituencies, meaning no need to redraw boundaries, and no overt erosion of the constituency-MP link.

In close three-way races the “compromise” candidate could be defeated in the first round even though they may be more broadly acceptable to the electorate than the top two candidates.

It penalises extremist parties, who are unlikely to gain many second-preference votes.

Lower preferences can potentially throw up a “lowest common denominator” winner without much positive support of their own.

It encourages candidates to chase second- and third-preferences, which lessens the need for negative campaigning (one doesn't want to alienate the supporters of another candidate whose second preferences one wants) and rewards broad-church policies.

A voting system that allows voters to rank candidates is prone to so-called 'Donkey voting', where voters vote for candidates in the order they appear on the ballot

It reduces the need for tactical voting. Electors can vote for their first-choice candidate without fear of wasting their vote.

It reduces the number of “safe seats” where the election result is a forgone conclusion