Song and English literature Glaswegian is unable mostly to take up (9)
I believe the answer is:
cantilena
'song' is the definition.
(I know that cantilena is a type of song)
'is unable mostly to take up' is the wordplay.
'is unable' becomes 'can't' (if you can't do something, you're unable to do it).
'mostly' means to remove the first letter.
'to' becomes 'til' (I've seen this in another clue).
'take up' becomes 'ena' (I am not sure about this - if you are sure you should believe this answer much more).
'til' with its first letter taken off is 'il'.
'cant'+'il'+'ena'='CANTILENA'
'and english literature glaswegian' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
(Other definitions for cantilena that I've seen before include "smooth flowing style" , "ballad" , "Melodic line" , "musical exercise" , "melodious music" .)