Not sure what is happening in the UK, but I watch prices pretty closely here and have noticed definate increases. Here, used car prices have risen across all makes and models, and this may be due to general economic conditions and new car prices in recent months. This being said, I follow Z4 prices for 2009+ 35i models and in the last 6-9 months, I have seen prices improve by 10% - 15% or so - more over the last year. Oddly, I see more cars for sale as well.