It is important to look for signs of the maker of a banjo. In this case someone in the past has taped a Gibson medium plectrum to the back of the banjo. And thus it has been listed on Ebay Uk as a Gibson Medium banjo!
I'm not sure what's more surprising, the fact that this can be called a Gibson because of the pick, or the fact that the BOAC label suggests there was a time you could put a banjo in an aeroplane hold without a case. Especially surprising for an instrument as rare as a Gibson Medium.