### Clue: preferably in case one's heading for referendum (6)
### Answer: SOONER 
 ### Explanation: Definition: preferably
 SO(in case;if, as in "so that happens, in that case you do this") + ONE **plus**(…'s;has) **the 1st letter of**(heading for) "referendum".
Answer: As in "I'd sooner die than do that!"