### Clue: across Before, it was on every 24; after, unavailable, it's frozen (4,6)
### Answer: POST OFFICE 
 ### Explanation: Definition: Before, it was on every 24
 POST(a preposition signifying "after";subsequent to) + OFF(to denote that an item in a menu is unavailable) + ICE(substance that is frozen).
Defn: A facility that formerly;before was in every High Street;answer to 24 across in town.