ADM1 is the code for 'first level administrative divisions' like states in the US. For cities you should use codes belonging to the featureClass 'P'. 'P' stands for 'populated place : http://ws.geonames.org/search?q=&country=GB&fclass=P
Thanks for the help. The only thing is this is too corse a granularity for me. I need to distinguish between diferent feature types within the catagory P. For example I need just the cities or just the towns, rather than all populated places.