Poet writes; 'special' Queen Elizabeth described! (7)
I believe the answer is:
spenser
'poet' is the definition.
(16th-century poet Edmund Spenser)
'writes special queen elizabeth described' is the wordplay.
'writes' becomes 'pens' ('pen' can be a synonym of 'write').
'special' becomes 'S' (common abbreviation as in Special Air Service).
'queen elizabeth' becomes 'ER' (abbreviation for Elizabeth Regina).
'described' indicates putting letters inside (written on the outside).
's'+'er'='ser'
'pens' placed into 'ser' is 'SPENSER'.
(Other definitions for spenser that I've seen before include "Edmund, 16th century poet" , "Author of "The Faerie Queen", d. 1599" , "Fairy Queen author" , "Edmund ---, Eliz. poet" , "Edmund - , sixteenth century English poet" .)