Someone pointed me towards the site Voter Power which purports to "demonstrate the increase in voter power that AV would bring." So I popped in the details for Lewisham Deptford, where less than year ago I spent a tough General Election.
This was the result;
Now, I'm grateful for the stats and all but I do think the the idea that my "voter power would increase by 33%" is slightly misleading as it goes from "fuck all influence" to "still fuck all influence". If you live in Lewisham Deptford your vote doesn't make any difference under either system. An increase of 33% makes it sound like there's be a meaningful change, when there hasn't.
This is the key problem with single constituency elections (and Presidential elections) in that it is a combination of winner takes all and a postcode lottery. Under both systems the votes of those who live in Lewisham Deptford simply do not give the people the same say as those who live in marginal constituencies - and even they, generally, are only getting a choice between two parties to misrepresent them.
Under proportional representation every voter's vote is of equal weight - no matter where they live. It also means that in Parliament every political position with significant minority backing has a voice. For me that's what democracy should be about, people's voices being heard - not one where only the biggest tribes are allowed to speak.