I wish I'd have good links on hand about the details of the organ harvesting bussines, but I read about it in a few (trustworthy) newspapers and don't know a good internet source. I don't think there's many people outside Chinese political circles denying it takes place, though.
As for using prisoner labor, I don't think we're talking about the same thing.
Many countries offer the prisoners a choice to reduce their sentence by working and this is a part of resocialization. Prisons will also have the inmates cook, clean and do all kinds of jobs around themselves for obvious reasons.
Now, if UK forces prisoners to work in order to make money on them, that's quite dreadful, but I'm suprised to hear it's the case...
(true, it's off-topic, we only touched China when discussing military spending... and even that's not related...)