Old fellows in charge, one wearing glasses by virtue of current position (2,7)
I believe the answer is:
ex officio
'by virtue of current position' is the definition.
'old fellows in charge one wearing glasses' is the wordplay.
'old' becomes 'ex'.
'fellows' becomes 'ff'.
'in charge' becomes 'ici' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'one wearing' is an insertion indicator.
'glasses' becomes 'oo' (OO looks like spectacles).
'ff'+'ici'='ffici'
'ffici' put into 'oo' is 'officio'.
'ex'+'officio'='EX-OFFICIO'
(Other definitions for ex officio that I've seen before include "By virtue of one's official position, Latin phrase" , "By right of office" , "By virtue of one's status" .)