Statement from UK spying agency (6)
I believe the answer is:
thesis
'statement' is the definition.
(thesis is a kind of statement)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for thesis that I've seen before include "A lengthy essay, perhaps for degree" , "He sits (anag) - treatise" , "Long research essay or treatise written for university degree" , "theory" , "Learned dissertation" .)