This tool allows you to search the Highways England database of roadside markerpost locations. You can download the raw data as an Excel spreadsheet from this location.
Use the map search to pinpoint a location and show markerposts within a 250m radius of that point. A maximum of 40 results will be shown within that radius.
Double-click the map to add a marker indicating the point of interest. Click the marker to remove it if you want to change its location.