In East, a significant police force once (5)

I believe the answer is:

stasi

'force once' is the definition.
(secret police of East Germany)

'in east a significant police' is the wordplay.
'in' indicates a hidden word.
'STASI' can be found hidden inside 'east a significant police'.

(Other definitions for stasi that I've seen before include "Former security force" , "old secret service" , "Force that spied" , "Secret police of the former German Democratic Republic" , "Former German security service" .)

I've seen this clue in The Times.

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