### Clue: Happier when Starmer after change of heart supports leaders of leftist unitary councils (7)
### Answer: LUCKIER 
 ### Explanation: Definition: Happier 
KEIR (Starmer) *after change of heart* becomes **K(IE)R, ***supporting *[*leaders of*] **L(**eftist) **U**(nitary) **C**(ouncils)