Ill-mannered detective imprisons one polite type (12)

I believe the answer is:

discourteous

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'ill-mannered detective imprisons one polite type' is the definition.
I can't judge whether this definition defines the answer.

'ill-mannered detective imprisons one polite' is the wordplay.
'ill-mannered detective' becomes 'ds' (detective sergeant. I am not sure about the 'ill-mannered' bit.**).
'imprisons' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'polite' becomes 'courteous' ('courteous' can be similar in meaning to 'polite').
'ds' placed around 'i' is 'dis'.
'dis'+'courteous'='DISCOURTEOUS'

Can you help me to learn more?

(Other definitions for discourteous that I've seen before include "Uncouth" , "Impolite" , "Ill-mannered" , "Rude, inconsiderate" .)

I've seen this clue in the Irish Times.

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