LSE explains various voting systems and provides the graph above showing how they would have changed the 2010 British election. More clarity here. As I understand the current Con-Lib referendum plan, it would be a move to AV, slightly increasing Liberal representation, and slightly reducing Tory representation. I'd vote for it. I care about maintaining a one-member-one constituency relationship. But I do think it has become deeply unfair under the current rules, and it's time for a change.