Grasses Blunt and Philby etc crossed England (5)
I believe the answer is:
reeds
'grasses' is the definition.
(type of grass plant)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for reeds that I've seen before include "Grasses at river's edge" , "River grasses" , "Stems for pens" , "Thatching stalks" , "Long grasses" .)