When creating a topology the geometry field cannot contain a Z coordinate.
OK but the Ordnance Survey Open Data highways layers containse a Z coordinate. Previously I had stripped this out using the latest version of QGIS which has a tick box in the front end that allows for import stripping of the z coordinate in the process. If you don’t have access to the latest QGIS version how can you strip out the z coordinates.
ALTER TABLE public.nuroadlink ADD COLUMN geom2(multilinestring,27700); UPDATE public.nuroadlink SET geom2 = ST_FORCE2D(public.nuroadlink.geom); ALTER TABLE public.nuroadlink drop column geom; ALTER TABLE public.nuroadlink RENAME COLUMN geom2 TO geom;