"Savills: Residential building land value drops 20pc"

Via Tim W comes this blindingly obvious bit of maths. At last year's peak, the typical price of a house related half to bricks/mortar and half to site value (or implied value of planning permission, same thing really). So if house prices have fallen 10% and bricks/mortar has remained constant, you'd expect site values, being a balancing figure, so have fallen by 20%.

Therefore, looking ahead, if house prices fall by one-third from the 2007 peak, site/land values will fall by two-thirds; if house prices fall by half, site/land values will be more or less wiped out.

Here's my chart showing how site/land values have changed since 1983:
For a fuller explanation, see here.