A month ago, I emailed Kent County Council's Highways department as follows:
I'm confused about the name(s) of the A225 road passing through Sutton at Hone. The Kent County Council Highways Gazetteer (March 2011) lists MAIN ROAD with a total length of 57.36 metres and DARTFORD ROAD with a length of 2156.95 metres. Yet there seem to be postal addresses ranging from 1 to 300 Main Road, Sutton at Hone, suggesting that the bulk of the road running through that parish is called Main Road, not Dartford Road. I wonder if you could check the accuracy of the listings in the gazetteer. The reason I am asking is that I am updating the map of the area for OpenStreetMap.org.
Today I received this reply from Dartford Borough Council:
It would appear that there is an error within the NSG as you claim. The numbering along the road would suggest that the change takes place on a 500m stretch of roadway either side of the railway bridge, towards the southern boundary of the Borough.
A site visit revealed no signage or road markings to provide a practicable start/end point that are recognisable on the ground, providing a simple route to correcting to the error. Several available datasets have differing opinions on the location of the change, from the railway bridge itself to 30m south to 300m south of that location.
I have been unable to get definitive documentation, for example a road adoption plan or section 38 agreement, to identify where the end of Dartford Road and the start of Main Road is at this time. This could be due to the road pre-dating a lot of this type of documentation and having been within the realm of several border changes.
I am seeking advice from Geoplace as well as the NSG custodians and others on the implications of making a change to the NSG without proper documented proof.
For your current need, I would suggest the station road junction 30m south of the railway bridge at OSGB36 555806, 169287 or WGS84 0°14'24.431"E 51°24'2.49"N would be a logical start end point.
I will update you when there have been further development.