In Britain, the Liberal Democratic Party, in its manifesto (the British equivalent of what we call a "platform" in America) for the 2005 election, stated:
Liberal Democrats in government in Scotland are already bringing in the single transferable vote (STV) system for local elections, so that local councillors will genuinely represent their community. We will extend this fair voting system to all local elections in Britain, and to the House of Commons, Scottish Parliament and National Assembly for Wales.STV is a form of proportional representation, about which I'll go into further detail in a later post.
One hope on the part of the Liberal Democrats is that, in the wake of a future general election, they will hold the balance of power in the House of Commons. In other words, if neither the Conservatives nor Labor has a majority in the House, but can form a majority in some sort of coalition with the Liberal Democrats (formal or informal), The Lib Dems could require concessions on proportional representation, as a condition for entering into such a deal.
The circumstances have not allowed for that in recent general elections. Labor has won majorities ranging from comfortable to monumental in the last three general elections. And current polls predict that the Conservatives will win a comfortable majority at the next general election, which will probably be held in 2010.
The platform of the Green Party of the United States includes the following: "We demand choices in our political system. This can be accomplished by proportional representation voting systems."
That party has no seats in Congress. And I doubt that they have very many, if any, in state legislatures. So, they're in even less of a position that the British Lib Dems to "demand" proportional representation.