Government action is also driving up the cost of land. In theory, it ought to be quite cheap: just 10pc of England's mass is developed, and that includes gardens, parks as well as homes, offices, roads and factories. There is lots of agricultural land left. Market prices back this up: in Oxford, a hectare of agricultural land with no planning permission is worth just £20,000. But that is where the planning rules come in: the same space is worth £1m with industrial planning permission and £4m with residential planning permission.