Ace leaving BBC is free (5)
I believe the answer is:
untie
'is free' is the definition.
(I've seen this before)
'ace leaving bbc' is the wordplay.
'ace' becomes 'a'.
'leaving' indicates named letters should be taken away.
'bbc' becomes 'auntie' (nickname for the BBC).
'auntie' with 'a' removed is 'UNTIE'.
(Other definitions for untie that I've seen before include "Release (knots)" , "resolve" , "Let loose" , "Disconnect; release" , "Release from bonds or open shoelace" .)