The Admiralty is not in this street (5)
I believe the answer is:
fleet
'this street' is the definition.
(Fleet Street is an example)
'the admiralty is not' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
The remaining letters 'flee' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for fleet that I've seen before include "Swift like navy" , "task force" , "Fast kind of armada?" , "Swift; armada" , "Navy - quick" .)