National symbol's a revelation, it's said (4)
I believe the answer is:
leek
'national symbol's' is the definition.
(emblem of Wales)
'a revelation it's said' is the wordplay.
'a revelation' becomes 'leak' (leak is a kind of revelation).
'it's said' indicates a 'sounds like' (homophone) clue.
'leak' is a homophone of 'LEEK'.
(Other definitions for leek that I've seen before include "Edible plant, Welsh symbol" , "Vegetable related to the onion" , "what Fluellen wore in France?" , "Bulb" , "English town" .)