As we run down the final straight in our campaigning against AV, here are some arguments you might consider using.
1) What we want in a healthy Parliamentary democracy is a governing party that has been elected on a clear programme, that has a sufficient majority to deliver that programme, but that faces scrutiny and challenge from a large and coherent opposition. What AV produces is either overwhelming majorities with very weak opposition, or hung Parliaments with governing programmes bearing little resemblance to what was promised at the Election.
2) AV encourages voters to vote against things, not in favour of things, by expressing preferences in favour of all their candidates but their most hated, regardless of what they know about those other candidates. That encourages negative politics and incoherent, bland political programmes, making it difficult for new ideas or new parties to break through or tough-but-necessary decisions to be taken.
3) AV advocates are wrong to claim that not having 50% of the vote makes MPs illegitimate. There is nothing magical about the number 50, and parliamentary democracy isn't about more than half the population wanting things. AV does not, in any event, guarantee that candidates have more than 50% of the vote. If (as is likely) people don't fill in preferences against every candidate, the winning candidate may have less than 50% of votes cast under AV.
4) AV's (not really) "50%" is nothing to do with proportionality. AV isn't proportional representation – indeed, most studies suggest that seats would be even less proportional under AV than under FPTP.
5) AV achieves its spurious (not really) "50%" of votes by re-allocating second or lower preferences of losing candidates. But it's hard enough to get enough information to know whether one prefers the incumbent or one's favoured alternate, let alone having any coherent opinion ranking one's fourth versus fifth preferences. Many people are likely to fill in their first and second preference, then simply run down the ballot in alphabetical order of votes aside from their most-hated candidate (e.g. anyone-but-Labour, or anyone-but-Conservative). That would mean that the result, in many constituencies, would depend on entirely randomly-allocated preferences.
6) AV advocates don't seem to know whether the 216 MPs elected in 2010 with more than 50% of the vote were the least legitimate (since they have the safest seats – safe seats being a Bad Thing according to AV advocates) or the most legitimate (since they are the MPs that have more than the mystically magic number 50% of votes).
7) AV won't end safe seats. It just means different safe seats. In addition to the 216 seats in which the winning candidate secured more than half the vote being presumably still safe, and the many other seats made safe by adding second preferences to already-large leads under FPTP, under AV there would be a new form of safe seat in which a candidate coming second or third would secure the vast majority of second preferences of candidates coming below her, and so always win the seat despite coming second or third on first preferences.
8) AV won't end tactical voting. It just means different tactical voting. For example, instead of expressing their genuine order of preferences, tactical voters will re-order their votes so as to try to achieve the early elimination of candidates the second preferences of which are likely to go to their favoured candidate and to keep in candidates whose voters are unlikely to have expressed second preferences.
9) Because AV results will take longer to count, it is likely that the results in many key constituencies will not be known on the night. This diminishes the important "theatre" of Election Night, and may well (after the initial glow of novelty wears off) mean lower turnouts.
10) Virtually no-one favours AV. It is only used internationally in Fiji and Papua New Guinea, with the Australians using a closely related system (but not the AV we have on offer here). (Contrary to Yes campaign claims, AV isn't the system used on the X Factor or the system used to elect Conservative Party leaders or the system used for the French Presidency. It just isn't – that's simply false. Those systems aren't even like AV (as, for example, the Australian not-quite-AV system is).) The Jenkins Commission set up by Tony Blair to look at electoral reform recommended against AV. Nick Clegg called it a "miserable little compromise". None of the leaders of the Yes2AV campaign favoured AV before this referendum. They merely hope we will vote for AV and then, finding it a bad system, seek to reform again. I agree with them – we would find it a bad system. So I'll be voting No.