In Currys in Cowley Road Uxbridge they had a TH42PZ85 for £799 which was the price I had expected a TH42PZ80 to be. The ticket said that it was in the sale that ends on Wednesday. They didn't have any 42PZ80s left, and said that there were none in the area as it is a discontinued model.
They are also doing free delivery and removal of your old TV until Wednesday.
I still haven't decided whether to go down the plasma or LCD route, but I hope this might help someone.