A lot is made of the fact that AV is not a proportional system (although in practise it does generally produce more proportional results than our present system). Yet AV could have a massive impact on voting patterns in the UK.
In fact I think the No team realise the impact AV will have more than the Yes team, which is why MPs in safe seats and councillors are pumping money into full page ads in the press and dominating the ads on the internet to try to persuade people to vote no.
In Australia they elect only 150 MPs compared to our 650 MPs at Westminster (changed to 600 for next election - an anti-democratic change). This means Australian constituencies are huge, 3 times the number of electors and geographically can cover huge areas (some of their constituencies are bigger than the entire UK!).
This has a disproportional effect, as the bigger the constituencies the less proportional the result (local elections in the UK are more proportional for this reason as wards are around a tenth the size of constituencies). This has kept Australian politics largely a two party affair as smaller parties need more resources to reach larger numbers of voters and more time and elections to overhaul the huge voting leads of the bigger parties.
The larger constituencies in Australia also explain why they have had less coalition government than the UK despite using AV.
So the proportional effects of AV are masked in Australia, where smaller parties are still in their fledging development.
In the multi-party UK, AV could have a massive proportional effect since there is enormous appetite to vote other than the big two. We can see this from the fact that even under FPtP a third of voters do this, most in the knowledge that their vote won't count towards the result, either their vote is completely wasted or they are playing the long game hoping a better result gradually over many years of elections will bring their smaller party into contention (it can be a long wait - many decades and fixing 5 year terms is another anti-democratic move of this government). In the latest PR Euro elections over 50% (55% to be precise) voted other than the big two.
Over time and elections, as people get used to AV, they will realise they are now free to vote as they please without having to make a choice between wasting their vote and having it count towards the final result. This is bound to encourage even more to venture away from the big two parties. No wonder the establishment MPs are so scared!