One that will flap and go on about new film (6)
I believe the answer is:
gannet
'one that will flap' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'go on about new film' is the wordplay.
'go on' becomes 'gan' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
'gan' placed around 'n' is 'gann'.
'gann'+'et'='GANNET'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for gannet that I've seen before include "A large diving sea-bird" , "Large diving sea bird" , "Large diving fish" , "Large seabird noted for its plunging dives for fish" , "Seabird - glutton" .)