It's beginning to look quite likely that we could end up with the Alternative Vote (AV) system. Aficionados of electoral reform will tell you that it's not a proportional system, which is quite true. The results it produces will be quite different from those produced by multi-member STV or d'Hont. That doesn't mean, however, that it would not be a significant change.
Unlike the multi-member systems, AV will continue to give small parties no seats. What AV does, however, is allow much more effective signalling by voters. It is very plausible that it could help small parties, over time, become big parties.
The point of AV is that it saves the voter from having to do tactical-voting calculations. Currently, anyone who votes UKIP, or Green, or SSP, or BNP is sacrificing their (tiny) influence on the result of the election in favour of making a public statement. With AV, you can do both - vote SSP ,Labour as 1 & 2, and there is less chance that your SSP vote will let in the Lib Dems. (Not no chance - there are still circumstances in which it might turn out that you would have got a different result by voting Labour, SSP, but they're complex and not very predictable)
2.5 million people voted UKIP last year. Only 900,000 did last week, so quite possibly the other 1.6 million didn't vote UKIP because of the wasted vote issue. If in the next general election, the constituencies which went 8% or 9% UKIP became 25% or 30%, they probably still wouldn't get any seats, but they'd get a lot more publicity, and they wouldn't be far short of getting MPs.
The same logic applies to high-profile candidates who defect from their parties to stand as independents. It becomes a straight popularity contest between them and the "official" candidate, since any supporter of the party can vote rebel-1 official-2.
AV might benefit the BNP most of all, since they have most to gain by giving voters a chance to anonymously show support for them. Today, nobody knows, do the BNP get only 2% because nearly everyone hates them, or because they're a small party and it's a wasted vote, or because most people think nearly everyone hates them, since they only get 2%? In the last case, it would only take a few election cycles for them to look less like outcasts to those who are secretly disposed to vote for them, but put off by the opprobrium.
At the end of the day, though, a politician will still win. I'm not paying all this attention because I think it's important, it's just more entertaining than the Premier League. But if you do care about who wins, then while multi-member STV is still the first choice, you probably shouldn't turn your nose up at AV.