Well, I've figured out the cause of the problem

I dismantled my clutch to see if there was some dirt or anything causing trouble, and it turns out that the clutch spring has snapped. I'm amazed it didn't make more of a mess in my clutch bell to be honest, quite a clean snap and no shrapnel anywhere.

So, if anyone else has a similar problem, you know where to look first

Any ideas if that's the kind of part that'll be stocked at my LHS, or will I have to get one ordered?

Thanks for the help all