In the UK we only vote on who will be representing the council or our member of parliament. We don't vote on propositions like you do. The last time we had ab referendum was in 1975. My daughter who is 18 voted for the first time today, but it was the first time either of us had voted in a referendum.
The AV vote as a piece of constitutional legislation should be looked at objectively, but the politics of it all just got in the way. There are three main political parties in the UK, Labour, Liberal Democrat and Conservative, but only two that have any chance of governing Labour and Conservative. Since Margaret Thatcher's term in office the Liberal Democrats have been viewed as the opposition to Conservative along with the main opposition Labour.
For Government we only vote for the legislative, and the political parties decide who the leaders are. In American terms it would be as if the Speaker of the House had all the powers of the president. When Tony Blair got in on a landslide, those constituencies where the liberals were in opposition to the Conservatives found that Labour supporters tactically voted Liberal Democrat to keep the Conservatives out.
During Labour's 13 years in office the Liberals positioned themselves even more left of centre, opposing the war in Iraq, and any form of tuition fees for students. In the last election the Liberals courted the student vote by signing a solemn pledge to oppose student fees. The last election resulted in a hung parliament. The Liberals went into coalition with the Conservatives, tripled student fees, and signed up to an austerity package and aseries of cuts more right wing than Thatcher. The price for all of this was the AV referendum.
People felt betrayed, the main beneficiaries of AV would be the Liberals. The Conservatives were against it anyway. So even though I am a Labour supporter, who intellectually supports AV I voted against it because I couldn't bear the thought of the Liberals being rewarded for basically lying to the electorate.