Spent a frustrating couple of hours today trying to gather missing street-names and confirming what I already suspected - that most of them were in inaccessible areas, namely the military base in Gillingham and Chatham Historic Dockyard. Spent two hours driving around and came back with three street-names. Anyway,I decided in the end to copy the ones on the military base from OS OpenData - StreetView in the first instance, Locator if necessary. Chatham Dockyard - I may pay the £15 to go in during normal visiting hours or I may try to get them to let me in for free by explaining what I'm trying to do.
Still thinking about the Contributor Terms. Have declined them for the time being while I make up my mind. I imagine I will accept them in the end.