Rather avant-garde poet's always collaring head of BBC 1 (6)
I believe the answer is:
edgier
'rather avant-garde' is the definition.
I can't tell whether this definition defines the answer.
'poet's always collaring head of bbc 1' is the wordplay.
'poet's always' becomes 'e'er' ('e'er' is a poetic term for 'ever' or 'always').
'collaring' means one lot of letters goes inside another.
'head of bbc' becomes 'DG' (abbreviation for Director-General).
'1' becomes 'I' (Roman numeral).
'dg'+'i'='dgi'
'eer' placed around 'dgi' is 'EDGIER'.
Can you help me to learn more?
(Other definitions for edgier that I've seen before include "More jittery" , "More nervous" , "More brittle" .)