Concealed assistance provided by data-gathering agency (6,7)
I believe the answer is:
secret service
'agency' is the definition.
(secret service is a kind of agency)
'concealed assistance' is the wordplay.
'concealed' becomes 'secret' (similar in meaning).
'assistance' becomes 'service' (service is a kind of assistance).
'secret'+'service'='SECRET SERVICE'
'provided by data-gathering' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for secret service that I've seen before include "Spying agency" , "Government agency" , "Government department involved in espionage" , "Hush-hush organisation" , "Spies' department" .)