Source
Department for Environment, Food and Rural Affairs. "Digest of Environment Statistics".
Description
Table 2 gives countrywide estimates for long term annual rainfall in millions of cubic metres together with the corresponding average runoff; the difference between the rainfall and runoff figures provides a measure of average evaporation losses. The data can be downloaded as a CSV, PDF or XLS file. (Data source: Centre for Ecology and Hydrology.)
Other Links
The Centre for Ecology and Hydrology (CEH) website
Provides information about CEH's seven designated data centres including the National Water Archive, responsible for NERC's hydrological data and for the National River Flow and Groundwater Level archives.
http://www.ceh.ac.uk/index.html