Hi, the sets you have mentioned are the best you will find for your budget, you should be pretty happy with them all, I'll just help you along a little with my thoughts. I haven't seen the Samsung so I can't really say much about it, although I have seen some reports of terrible image retention (worse than the LGs) on the new models, whether this is a problem with individual sets or the entire range I'm unsure though. Owners have commented on a decent picture though. But my general advice would be to look at the B450, it's the 2009 model (although this is the model I've seen image retention problems with, but last years models weren't great for image retention either).
So, comparing the C10 and PQ3000 there isn't much between them, but I think the PQ3000 is a bit better. Basically the C10 is a mix of Panasonics 2008 and 2009 plasmas, the PX80 (2008) and the X10 (2009), there wasn't much of a jump in technology between the two so you do get a very good TV, but I think the LG, which uses all the 2009 LG technology, is the better choice unless you're going to be spending a lot of time gaming, watching news channels (or any other channels with bright static images) or using it as a PC monitor. If you're going to be doing any of those things then you should discount the LGs as they are more prone to image retention, a little bit of those uses is fine, but if you do it for more than a few hours at a time regularly then you should steer clear.
So, one of the big advantages of the LG is the fact that it has expert picture controls, you can get the exact picture you want as it offers full calibration controls including white balance and all the colour controls, the Panasonic offers you contrast, brightness, colour and sharpness, so you don't get quite as much 'fiddle-ability'. Overall I think the LG handles motion and low quality SD channels a bit better too. It's a very similar case between the X10 and PQ6000 but it's a little closer, I still prefer the LG slightly, but again, the Panasonic is more resistant to image retention.
The difference between the PQ3000 and PQ6000 is mainly in the sound, the 6000 has fairly significantly better sound, and is worth the extra bit in my opinion, unless you're going to be connecting it to an external system (in which case make sure you can connect via optical). There are also a few features snipped off the USB inputs and the design isn't frameless like on the PQ6000 (there isn't a sheet of glass covering the screen). The difference between the X10 and C10 is more significant but there's still very little in it, overall I would say that the X10 is probably worth the extra £40.
So, to sum up. The PQ6000 gets my vote, closely followed by the X10 (very closely) but if you're connecting to an external system then get the PQ3000, unless you're going to be using the USB features or like the design of the 6000.
hope that helped