Clue: Vigorously approve of crooks kidnapping French drunk (4,11)
Answer: LIKE GANGBUSTERS
Explanation: Definition: Vigorously
LIKE (approve of) + BU (French for "drunk" – past participle of "boire", as in *j'ai bu du vin*). Although I was familiar with this expression, I didn't know that it came from an American radio programme that ran from 1936 to 1957.