Choosing how best to cast your vote under AV is actually considerably more complex than many imagine. I agree with the proponents of AV in that it is relatively easy for voters to rank candidates in preferential order. This is not the issue. The problem with AV is that it creates circumstances in which people should strategically cast dishonest votes.
Under FPTP the only way a Conservative supporter can ever help the Conservative candidate win in a constituency is by casting a vote for the Conservative candidate. It is true that many voters decide to give their support to the candidate most likely to oust the incumbent as opposed to their preferred candidate. Nonetheless in these circumstances they still make their vote understanding that they will increase the vote total of the candidate they voted for by one.
Under AV however, there is the possibility that by casting your first preference for the Conservative candidate, you will cause a Liberal Democrat victory; whilst by casting your first preference for the Labour candidate, you will cause a Conservative victory. That’s right: vote Conservative, get a Lib Dem MP, vote Labour, get a Conservative MP. Don’t believe me? It seems too ridiculous to be true doesn’t it?
This situation can come about by the fact that your vote plays a part in determining which preferences of the other voters are counted as their votes. When you vote for the Conservative candidate therefore, there is no guarantee you will increase the Conservative’s total amount of votes by one. Your vote for the Conservative candidate could end up decreasing the total amount of votes that the candidate receives! In technical jargon AV can sometimes cause the monotonicity criterion to violated. Roger Mortimore has blogged a good example of how such a scenario might occur, but there are many more.
Now it must be acknowledged that such a situation will not occur all the time. It will normally be the case that as a Conservative supporter you should cast your first preference for the Conservative candidate. The problem is that when you vote, you will be unaware as to what circumstances are prevalent. That is to say that you won’t know whether you need to vote Labour or Conservative to get a Conservative MP. Imagine entering a polling both only to discover that the candidate names on the ballot paper were written in hieroglyphics. This is the plight of the AV voter. Forget past stories of politicians breaking promises, in this case you literally have no idea what you are voting for. How can that be democratic?
Whilst I’m by far not the first to discuss tactical voting under AV, this is an issue which needs more attention. For instance fullfact.org – a website supposed to be an independent fact-checking organisation, says that under AV, “people will not need to vote tactically for their first choice candidate”. Too many people genuinely believe that AV is a system that allows you to vote with your heart and your head. It is this which I hope to have illustrated as patently false.