Over at the LSE British politics and policy blog, Professor Patrick Dunleavey raises an interesting point about the referendum on electoral reform. There are, he says, two forms of the "Alternative Vote", the system the Conservatives and Liberal Democrats are committed to delivering under the terms of the Coalition Agreement - Australian AV and the form of AV used to elect the London mayor (often known as the Supplementary Vote). In the debate so far:
Most people think of the Australian version of AV described in our Simple Guide to Electoral Systems. But there is a simplified and British version of AV that has been used very successfully in London to elect the Mayor (where it is sometimes called theSupplementary Vote). Here people can express a first preference (marking an X in a first preference column) and a second preference (marking a second X in their second preference column. They do not need to use numbering, which makes it easier to run this voting method alongside other elections that use X voting – like the European Parliament, Scottish and Welsh Assembly, the London Mayor and Assembly elections, and the English local government elections.
Dunleavey highlights what he considers to be distinct advantages to the London form of AV which "creates a run-off between the top two candidates in a local constituency." By contrast under the Australian form of AV it is theoretically possible (though unlikely) "that candidates initially placed third, fourth or even fifth in the electorate’s first choice preferences could none the less end up defeating higher order candidates. What is more, the views of people who cast many preferences by numbering all the candidates can have more weight in determining the result than people who only cast a couple of preferences."
There are, he argues, also tactical reasons why the London form of AV should be favoured by electoral reformers. Dunleavey thinks that London AV will be less threatening to Tories than the Australian kind since it has already been used successfully to elect a Tory mayor and it is less likely to be seen as the thin end of a wedge to bring in PR since it "restricts potential winners to the top two parties".
But that, surely, is part of the problem and why - despite the supposed tactical advantages of going for the London system - the Lib Dems shouldn't now start advocating another type of AV. As MatGB points out in the comments, London AV isn't fully preferential and forces voters to use guess work to work out who will be in the final round so that they can then cast their second vote for one of them. If anything, this would probably reinforce the two party duopoly rather than break it open. It seems unlikely, therefore, that Lib Dems will now start talking up the London system. Being more specific on the date of the referendum in the Coalition Agreement, on the other hand, would have been a very good idea, as Clegg is now discovering.