Critic regularly irked Spectator (8)
I believe the answer is:
reviewer
'critic' is the definition.
(reviewer is a kind of critic)
'regularly irked spectator' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'spectator' becomes 'viewer' ('viewer' can be a synonym of 'spectator').
The alternate letters of 'irked' are 're'.
're'+'viewer'='REVIEWER'
(Other definitions for reviewer that I've seen before include "Critic" , "Writer who reports and analyses" , "One should be critical" , "critical sort" , "Writer who assesses the merits of a book, play etc." .)