Many recognize MI5 and MI6, some MI9. All these are services of Military Intelligence [disregard the picture...]. Here they are, organised, as they were during WW2:
MI 1 Administration.
MI 2 Information on Middle and Far East, Scandinavia, USA, USSR, Central and South America. MI 3 Information on Europe and the Baltic Provinces (plus USSR, Eastern Europe and Scandinavia after Summer 1941).
MI 4 Geographical section - maps (transferred to Military Operations in April 1940).
MI 5 Liaison with Security Service. Some Portuguese Axis controlled spies where caught in the UK by MI 5.
MI 6 Liaison with SIS. Section V of MI 6 had an office in Lisbon during WW2.
MI 7 Press and propaganda (transferred to Ministry of Information in May 1940).
MI 8 Signals interception and communications security.
MI 9 Escaped British PoW debriefing, escape and evasion (plus enemy PoW interrogation until December 1941). There was a station of MI 9 in Lisbon during WW2.
MI 10 Technical Intelligence world-wide.
MI 11 Military Security.
MI 12 Liaison with censorship organisations in Ministry of Information, military censorship.
MI 13 Not Used.
MI 14 Germany and German-occupied territories (aerial photography until Spring 1943).
MI 15 Aerial photography (in Spring 1943 aerial photography moved to the Air Ministry and MI 15 became air defence intelligence).
MI 16 Scientific Intelligence (formed 1945).
MI 17 Secretariat for Director of Military Intelligence (from April 1943).
MI 18 Not Used.
MI 19 Enemy PoW interrogation (formed from MI9 in December 1941).
MI (JIS) Axis planning staff.
MI L (R) Russian Liaison.
MI L Attachés.