You mentioned this before and I must admit I do think you are onto something with the importance of a future Labour govt being a success, as I do think otherwise something more radical will be looked at.
I don't think parties on the rise across Europe are actually as many on the left would characters them (see my post above) but they are clearly something different from the status quo of centre-right and centre-left post-war western European governments.
I don't think Labour will be any more of a success than the current govt btw, because as I've consistently said, we keep misdiagnosing the problem, so we won't solve those problems, so make of that what you will, but that's another thread entirely.