Excessively particular lover of old ham sandwiches (9)

I believe the answer is:

overexact

'excessively particular' is the definition.

'lover of old ham sandwiches' is the wordplay.
'lover of old' becomes 'ex' (an ex-lover).
'ham' becomes 'overact' (synonyms).
'sandwiches' means one lot of letters goes inside another (to sandwich is to block something in).
'ex' put inside 'overact' is 'OVEREXACT'.

I've seen this clue in The Times.

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