A new article published by the BBC detailing the area built on by district may interest you.
Not surprisingly, 100% of the City of London is built on, but nationally the figure is 6%. Birmingham at 68% and Manchester at 67% are substantially covered whereas only 29% of Leeds is built on. Of the four home nations, Scotland is the less built on at only 2.1% although Glasgow at 62% is comparable to the big English cities.
Across the UK, about 57% of land is used for farming, 35% is considered natural and about 2.5% green urban. If your looking for a natural environment, head up to the Scottish Highlands, with a chart topping 90%. Richmond Park, one of the great parks near London, helps Richmond on Thames win the green urban crown at 58% coverage.