S.O. pen holder

S.O. pen holder with nib, a photo by polydaktyl on Flickr.

A thorough de-rusting of the metal bit of the pen holder revealed that said writing instrument was indeed one for the HMSO collection.
Marked:
S [crown] O
Code No 49-14
fitted with a steel pen by Arnold, marked
"Student Pen
AJ Arnold & Son Ltd
Leeds"