Representative and politician engaged in commercial activity (6)
I believe the answer is:
sample
'representative' is the definition.
(sample is a kind of representative)
'politician engaged in commercial activity' is the wordplay.
'politician' becomes 'mp'.
'engaged in' indicates putting letters inside.
'commercial activity' becomes 'sale' (I've seen this in other clues**).
'mp' going inside 'sale' is 'SAMPLE'.
'and' acts as a link.
(Other definitions for sample that I've seen before include "Small part intended to represent the whole" , "Small representative piece" , "Small part representative of the whole" , "Test the specimen" , "piece to try" .)