One of the arguments the No side make is that AV will let BNP voters have a greater say.

MYTH – Will AV help to shut the doors on extremists like the BNP?
REALITY – No. Extremists like the BNP, the National Front, and the British Union of Fascists have never had an MP elected under our current system. But while we hope that AV still wouldn’t lead to extremist parties winning seats, it would certainly give them more influence. AV undermines the fundamental principle of One Person, One Vote, and rewards people who vote for fringe candidates by making them the first to get another vote counted. In some seats, BNP supporters could get at least six chances to have their vote counted – while mainstream voters would only get their vote counted once. Because the other parties would need extra votes in later rounds of counting, they’d have an incentive to pander to the extremists to try and win their second preferences.
No2Av.org

So I took the results from the 2010 General Election and made several assumtions.

1. That the votes cast were for everyone’s first preference and that no one had voted tactically
2. That the two parties with the most votes made it to the final stage

I then

1. Ingored Northern Ireland
2. Excluded constitencies where the winner already reached the 50% threshold.
3. Counted the number of votes which could be transferred from voters of each Party

So here are the results

So this means that the big three parties will need to pander to the votes of the other big parties, more than that of the BNP or NF.