Speech beginning as follows: "Shut up" (4,2)

I believe the answer is:

stow it

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'follows shut up' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'speech beginning as' is the wordplay.
'beginning' indicates taking the first letters.
'as' becomes 'towit' (I can't justify this - if you can you should believe this answer much more).
The first letter of 'speech' is 's'.
's'+'towit'='STOW IT'

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I've seen this clue in The Independent.

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