### Clue: Youngster's tucked into cake and salad as a working rule (10,3)
### Answer: PARKINSON’S LAW 
 ### Explanation: Definition: working rule
 SON(a youngster)'S **contained in**(tucked into) PARKIN(a type of dark gingerbread originally from the north of England) **plus**(and) SLAW(coleslaw/a salad dish of raw cabbage, carrots and other vegetables).
Defn: The adage "work expands so as to fill the time available for its completion".