Some years ago (circa 1990) I purchased the four CDs which make up a digital chart of the world. The data in these CDs forms a 1:1000000 scale vector basemap of the world in VPF format. The primary source for this data is the US Defense Mapping Agency Operational Navigation Chart (DNC) series. While the data does contain some British Crown Copyright data, the CD license states that " these data in their DCW form may be freely reproduced and adapted".
Does this mean I can use this database as a ‘copyright free’ reference?