What fire drill's doing at Westminster finance office? (8,5)
I believe the answer is:
clearing house
'office?' is the definition.
The answer and definition can be both groups as well as being singular nouns.
Perhaps there's an association between them I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for clearing house that I've seen before include "What eases flow between banks" , "preparing to move to another building?" , "Banking establishment" , "Central collection place for financial transactions" , "Financial agency" .)