Lecturers study royal protocols at last (7)
I believe the answer is:
readers
'lecturers' is the definition.
('reader' can be a synonym of 'lecturer')
'study royal protocols at last' is the wordplay.
'study' becomes 'read' ('read' can be a synonym of 'study').
'royal' becomes 'er' (I've seen this in other clues).
'at last' indicates one should take the final letters.
The final letter of 'protocols' is 's'.
'read'+'er'+'s'='READERS'
(Other definitions for readers that I've seen before include "bookworms" , "Perusers of the written word" , "Senior lecturers" , "cheaters" , "Book users" .)