The UK is fortunate to have a range of increasingly accurate height data-sets available. These are as follows:
Ordnance Survey Terrain 50
Ordnance Survey Terrain 5
NEXTMap® 5m DEM
LIDAR 2m, 1m, 0.5m, 0.25m
Additionally we normally commission a site topography survey for projects giving highly accurate height data.
As well as Landform data-sets we have Surface data sets available. Such data-sets include surface elements such as buildings and vegetation. However it must be noted that the accuracy of vegetation is very poor as the remote sensing technique fails to pick up top of tree canopies. But for solid bjects, such as buildings these can be very accurate.