### Clue: Official in black and blue eats in the City dining room (9)
### Answer: REFECTORY 
 ### Explanation: Definition: dining room
 [ REF(short for "referee", an official in a competitive match, traditionally wearing black) **plus**(and)TORY(informal name for a Conservative Party member, traditionally represented by the colour blue) ] **containing**(eats) EC(abbrev. for for "East Central", the post-code area that includes all of the City of London).