Twickenham's first comedian embracing northern regional accent (5)
I believe the answer is:
twang
'regional accent' is the definition.
(thesaurus)
'twickenham's first comedian embracing northern' is the wordplay.
'first' indicates taking the first letters.
'comedian' becomes 'wag' (I've seen this before).
'embracing' means one lot of letters goes inside another.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
The initial letter of 'twickenham' is 't'.
'wag' enclosing 'n' is 'wang'.
't'+'wang'='TWANG'
(Other definitions for twang that I've seen before include "A nasal intonation in speech, or sound of guitar" , "Nasal or musical sound" , "Sharp vibrating sound" , "Nasal quality - strumming noise" , "ringing sound" .)