Sour old company porter’s English language dull and verbose? (11)
I believe the answer is:
officialese
'language dull and verbose?' is the definition.
(boring, official vocabulary)
'sour old company porter's english' is the wordplay.
'sour' becomes 'off' (synonyms).
'old company' becomes 'ici' (former company Imperial Chemical Industries).
'porter's' becomes 'ale's' (type of beer).
'english' becomes 'E' (abbreviation).
'off'+'ici'+'ales'+'e'='OFFICIALESE'
(Other definitions for officialese that I've seen before include "bureaucratic language" , "Formal language" , "Bureaucratic verbiage" , "Pompous language" .)