Also known as the Marshalls Geo Disc, these were part of the Geo Street range of street furniture. The range was not limited to street lighting, but included things such as: benches, bike parking, bollards, junction islands, and many more items. The Geo Disc 750 was a larger version of the 400, which (I believe) equates to their diameter in mm.

Birmingham

These examples are located outside of Suffolk Place, mounted at 8m.

I believe these examples run SON-T and CityWhite lamps, probably 150W given the 8m mounting-height and wide road.

Another example further down the road: