Ridiculously stern peer who introduces radio show? (9)
I believe the answer is:
presenter
'who introduces radio show?' is the definition.
(radio presenter)
'ridiculously stern peer' is the wordplay.
'ridiculously' indicates anagramming the letters (I've seen this in other clues).
'stern'+'peer'='sternpeer'
'sternpeer' anagrammed gives 'PRESENTER'.
(Other definitions for presenter that I've seen before include "Broadcast introducer" , "Disc jockey" , "anchor?" , "TV person" , "Compere" .)