I have now created new point data for about 6,000 settlements in Cornwall (with more accurate Lat/Long coordinates than provided by the Ordnance Survey Open Names dataset) since this is only accurate to +/- 1 km.
The next step is to add elevation data (height above sea level in metres). For this I am again using OS data, this time accurate to 50m, which is good enough for my purposes. Problematically, this data comes in a large number of files, organised in grid squares, units in metres, so several steps may be required before I can integrate this with my Lat/Long place names data.
The OS national grid squares for Cornwall and Scilly are all of SW and SV, and parts of SX and SS.