TV alien you wouldn't want to drop? (7)
I believe the answer is:
clanger
This clue is a double definition.
'tv alien' is the first definition.
(reference to children's TV show The Clangers)
'you wouldn't want to drop?' is the second definition.
(to drop a clanger is to make a blunder)
(Other definitions for clanger that I've seen before include "Big blunder" , "Big mistake (when dropped)" , "Bell possibly" , "Embarrassing mistake (colloq.)" , "A slang blunder - drop it" .)