He prohibits a flag (6)

I believe the answer is:

banner

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'a flag' is the definition.
(banner is a kind of flag)

'he prohibits' is the wordplay.
'he' becomes 'Ban'.
'prohibits' becomes 'ner' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ban'+'ner'='BANNER'

Can you help me to learn more?

(Other definitions for banner that I've seen before include "Large fabric sign" , "Ensign" , "Pennant" , "Queen brought in British flag" , "Streamer, flag" .)

I've seen this clue in The Daily Express.

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