This projection is specifically used to convert between ETRS89 and Ordnance Survey® British National Grid using the OSTN02® transformation.
The National Grid Transformation OSTN02 is an interpolated grid of horizontal plane shift parameters covering GB at 1-km resolution, which converts ETRS89 GPS coordinates to National Grid coordinates with an accuracy of 20 cm (RMS). It takes no projection-specific parameters.
Note: Users should not normally have to use this projection to define their own systems – FME ships with the OSGB-GPS-2002 coordinate system, which is based on this projection.