Wretched old Tory right-wingers holding back (6)
I believe the answer is:
Here is my best explanation:
'wretched' is the definition.
'old tory right-wingers holding back' is the wordplay.
'right-wingers' suggests the final letters (the rightmost letter in the word).
'holding' is an insertion indicator.
'back' becomes 'rear' ('rear' can be a synonym of 'back'**).
The final letters of 'old tory' are 'dy'.
'dy' enclosing 'rear' is 'DREARY'.
(Other definitions for dreary that I've seen before include "Dull and cheerless", "Cheerless and dull", "Dismal, funeral", "Bleak, depressing", "Dark", "Banal", "Dismal and gloomy", "Overcast", "Gloomy and dismal" and "avoiding exciting stuff".)