Crossword Genius

Firebrand with clout in King Edward, say? (3-7)

Ross

I believe the answer is:

tub-thumper

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'firebrand with clout' is the definition.
I can't judge whether this defines the answer.

'in king edward say?' is the wordplay.
'in' is an insertion indicator.
'king edward' becomes 'tuber' (King Edward is a type of potato).
'say?' becomes 'thump' (I've seen this before).
'tuber' going around 'thump' is 'TUB-THUMPER'.

Can you help me to learn more?

(Other definitions for tub-thumper that I've seen before include "Declamatory public speaker" , "Ranting supporter of a cause" .)

I've seen this clue in The Times.
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