Perrins' partner in sauce (3)
I believe the answer is:
lea
'perrins' partner in sauce' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lea that I've seen before include "''The lowing herd winds slowly o'er the ... '' (Gray)" , "Pasture, London river" , "Grass area" , "Poetically, a piece of meadow or pasture" , "River flowing through London" .)