1. A geolocation data storage system for communication session data from a mobile radio communications network, the mobile radio communications network supporting mobile communication units, the geolocation data storage system comprising: a first storage area, the first storage area operable to store a record of data for each communication session taking place in at least one geographical region of the mobile radio communications network; a first processor, the first processor operable to access the stored record of data for each communication session, to identify a subset of the data for each communication session, and to calculate geolocation information for each communication session; and a second storage area, the second storage area operable to store the subset of the data for each communication session, and the geolocation information for each communication session; wherein the geolocation data storage system is configured to delete the record of data for the communication session from the first storage area after a pre-set time limit, and retain the subset of data in the second storage area beyond the time limit.