Covers Sylvia's first with Ted Hughes's last (7)
I believe the answer is:
sheaths
'covers' is the definition.
(sheath is a kind of cover)
'sylvia's first with ted hughes's last' is the wordplay.
'sylvia's first' becomes 's' (1st letter of 'sylvia').
'with' is a charade indicator (letters next to each other).
'ted' becomes 'Heath' (Ted Heath, UK prime minister 1970-74).
'last' suggests the final letters.
The final letter of 'hughes' is 's'.
's'+'heath'+'s'='SHEATHS'
(Other definitions for sheaths that I've seen before include "Protective covers" , "Cases" .)