Believed on both occasions one hadn't acted rashly (7,5)

I believe the answer is:

thought twice

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'occasions one hadn't acted rashly' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'believed on both' is the wordplay.
'believed' becomes 'thought' ('think' can be a synonym of 'believe').
'on both' becomes 'twice' (I can't justify this - if you can you should give a lot more credence to this answer).
'thought'+'twice'='THOUGHT TWICE'

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I've seen this clue in the Evening Standard.

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