The BC41 knife is known to be issued to the British Commandos and appears in the SOE manual of equipment with lots of examples turning up in Norway with a history of being Norwegian Resistance.
The BC remains a mystery but some sources quote it as meaning Bliss Casters or Birmingham Casters with 41 being the date. It is made of cast iron.
There are no makers markings other than the same BC41 but there is a WW2 period commercial knuckle knife with a different style of knuckleduster grip in brass made by James Ryalls & Co of Sheffield which has an identical size and shape blade even down to the position and style of the three grip rivets. Even the scabbard is identical. James Ryalls is almost certainly the cutler and assembler of the BC41 knife.
John Pidgeon