ID of London photographic company

[Brett Payne]

I am trying to identify the London company which created two very big charcoal-coloured royal portraits based on photographic enlargements of Prince George (later King George VI) and Princess Mary. As shown in the attached image, the initials are either PM Co. or MP Co. of London. The portraits themselves appear to have been taken around 1893, shortly before or soon after their marriage, and the hand-coloured enlargements some time between then and 1905.

I've searched both the online photoLondon database and Michael's physical directory for candidates in the "M" and "P" sections without success. Maull and Polyblank, who might have been in the game, were out of business as a partnership by 1865ish, long before these were made. They seem to be semi-official portraits, since they were hanging for some years in the old Parliament building in Wellington, New Zealand.

Does anyone have any ideas, please?

[Brett Payne]