I disagree, BeeenBeta - I think Labour have alienated a lot of their core vote, and there is a massive split in the centre left. And the Conservatives have moved a lot closer to the centre, too. All of which, imo, argues for Proportional Representation. The closer to the centre the parties come, the less argument, imo, for first past the post.
Wem - in answer to your question. If you assume that both Cons and Lab have lost an equal number of the votes to Libs, you're still looking at either a Con or Lab MP in your area, because the swing to Libs would have to be immense in you area. Though, who knows, it might be immense - I haven't any idea how the canvassing is going.
If you assume that the Libs are picking up voters from mainly Lab supporters in you area, which is probably more likely, you are looking at a Con MP. Unless all those potential Lib voters vote Lab.
I think.
But you're right - it's your vote. If you feel strongly for one party, or one candidate, this is your chance to make that feeling known. In fact, pretty much your only chance (!) so ... .