BBC informally dropping a release (5)
I believe the answer is:
untie
'release' is the definition.
(eg to untie restraints)
'bbc informally dropping a' is the wordplay.
'bbc informally' becomes 'auntie' (Auntie is a nickname for the BBC).
'dropping' is a deletion indicator.
'auntie' with 'a' taken away is 'UNTIE'.
(Other definitions for untie that I've seen before include "Release (knots)" , "Let loose" , "Release, loosen" , "Unite (anag)" , "Release bindings or shoelaces" .)