On second thoughts, this may well be an interesting gun, based on the description of the markings.
W Greener was a dyed-in-the-wool proponent of the muzzle loader and held strong views against the breech loader, and was disinclined to build them.
WW Greener, son of WG, was apprenticed to his father's firm, but held opposite views, and very much favoured the new system. I believe that WW , in association with a brother, marketed a few guns under a London address, under the Greener name. Presumably WWG would have had these guns constructed by outworkers and then sold on as a back door business.
WG and WWG parted company on ( I believe acrimonious terms) and it may be that the sons' side dealings brought things to a head. The old man would not countenance guns bearing the Greener name being sold outwith his own control.
Subsequently WWG adopted a similar stance to his brother J Greener who put out a few guns under his own initiative... and it is reported that WW "escorted" Joseph to the docks and ensured his departure ...westward !!
So- the hammer style of the above gun and the style of maker name and address point to this scenario. Does the gun have a serial number?