Articles by retired chap about Brussels club? (9)
I believe the answer is:
athenaeum
'club?' is the definition.
(London private members' club)
'articles by retired chap about brussels' is the wordplay.
'articles' becomes 'athe' (two examples of the part-of-speech: a+the).
'by retired chap' becomes 'nam' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'brussels' becomes 'EU' (European Parliament is based in Brussels).
'nam' placed around 'eu' is 'naeum'.
'athe'+'naeum'='ATHENAEUM'
(Another definition for athenaeum that I've seen is " London club for the learned".)