Old magistrate altered a report (7)

I believe the answer is:

praetor

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'old magistrate' is the definition.
'praetor' can be an answer for 'magistrate' (praetor is a kind of magistrate). I am not certain of the 'old' bit.

'altered a report' is the wordplay.
'altered' indicates anagramming the letters.
'a'+'report'='areport'
'areport' anagrammed gives 'PRAETOR'.

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I've seen this clue in The Guardian.

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