Yes, there has been a bit of a swing back to a two-party system. Which again makes the premise of khandro's post flawed. Outside Scotland and Northern Ireland, there are currently only two parties worth voting for in almost every seat bar a handful. So if you don't like whoever your current MP is, or whoever your current government is, then essentially your best chance of bringing about change is to vote for the other one -- if you bother to vote at all, that is.
All of this is lost at the ballot box, which sees no difference between grudging protest votes and wholehearted support. Sadly, perhaps, Corbyn won't see that either. He might be right in one sense: as long as the current Tory government continues to show a reverse Midas touch, then support for Labour will grow as the only viable alternative, and Labour can look forward to reasonable chances of being in government in 2022.
That doesn't mean that suddenly there is support for socialism, though. But anyway, as kromo points out, there's more to socialism than its Communist bigger brother anyway.