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The Chief of the Secret Intelligence Service serves as the head of the Secret Intelligence Service (SIS, also commonly known as MI6), which is part of the United Kingdom intelligence community. The Chief is appointed by the Foreign Secretary, to whom he directly reports. Annual reports are also made to the Prime Minister.[1]
The chief of the Secret Intelligence Service typically signs letters with a "C" in green ink.
https://en.wikipedia.org/wiki/Chief_of_the_Secret_Intelligence_Service
The Foreign Secretary also has ministerial oversight for the Secret Intelligence Service (MI6) and the Government Communications Headquarters (GCHQ).
https://en.wikipedia.org/wiki/Secretary_of_State_for_Foreign_and_Commonwealth_Affairs
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