Burial place of old British missile (6)
I believe the answer is:
barrow
'burial place of old' is the definition.
(historical type of burial mound)
'british missile' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'missile' becomes 'arrow' (arrow is a kind of missile).
'b'+'arrow'='BARROW'
(Other definitions for barrow that I've seen before include "Cart for the river?" , "Handcart; burial mound" , "such as street-trader might have?" , "Small hand-propelled cart" , "Northern town" .)