Difference between the MI5 and the MI6

By: | Updated: Dec-18, 2017

The MI5 and the MI6 are very important military agencies responsible for protecting the UK against potential threats. There are several differences between these two agencies that this article seeks to highlight.

Summary Table

Also known as the Security Service Also known as the Secret Intelligence Service
By definition, focuses on domestic counter-intelligence operations, counter-terrorism, and espionage By definition, focuses on foreign or external threats
Accountable to the Home Secretary Answers to the Foreign Secretary
Headquartered in the Thames House in London Headquartered in Vauxhall Cross, Lonodon


MI5 insignia
The MI5 insignia

The MI5, or Military Intelligence, Section 5, is the United Kingdom’s Security Service, forming part of the territory’s intelligence machinery. The main role of this organization is to conduct domestic counter-intelligence and security operations. MI5 works alongside GCHQ (Government Communications Headquarters), Defence Intelligence, and the Secret Intelligence Service. Headed by the Joint Intelligence Committee, MI5 is tasked to protect and preserve British parliamentary democracy and its economic interests. In the UK civil service community, MI5 is also called Box 500, after its wartime address PO Box 500. The organization is currently located in Thames House, London.

The MI5 is focused on several key responsibilities. Their top priority is to respond to both local and foreign terrorism. The organization reportedly spent 65% of its 2014 budget on foreign counter-terrorism while the rest of the budget was allocated on domestic terrorism and counter-espionage. It is also the MI5’s responsibility to respond to subversion and counter the production of WMD’s (or weapons of mass destruction).

MI6 insignia
The MI6 insignia

The MI6, otherwise known as the Secret Intelligence Service (SIS), is Britain’s foreign intelligence agency. It stands for Military Intelligence, Section 6. Its head, the SIS chief, answers to the Foreign Secretary. The MI6’s existence was kept secret for 85 years until it was formally acknowledged by the British government in 1994. It is part of the United Kingdom’s intelligence machinery along with GCHQ, Defence Intelligence, and MI5. The SIS is currently headquartered in Vauxhall Cross, London.

Founded in 1909, MI6 was derived from the Secret Service Bureau. It was established as a means to control domestic and overseas covert intelligence operations. The bureau was divided into army and navy sections, which eventually concentrated on internal and foreign counter-espionage works, respectively. In 1916, the foreign section of the bureau was designated the Directorate of Military Intelligence Section 6. The first MI6 director was Captain Sir George Mansfield-Cumming. He usually signed letters by affixing the letter “C” in green ink. This practice was adopted by subsequent SIS directors when signing documents.

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MI5 vs MI6

So, what’s the difference between the MI5 and the MI6? The British Military Intelligence or MI used to be composed of numbered agencies that ran up to 19. During the post-World War II era, most of these agencies were consolidated into the MI5 and MI6.

MI5 stands for Military Intelligence, Section 5, and is the United Kingdom’s Security Service. It deals with gathering information and conducting operations domestically to protect the United Kingdom and its people against foreign threats or international terrorist activities. MI6 or Military Intelligence, Section 6, is otherwise known as the UK’s Secret Intelligence Service (SIS). This agency focuses on foreign or external threats. The MI6 is often described as the UK’s equivalent to the CIA, whereas, MI5 is often compared to the National Security Agency of the US. The MI5 is answerable to the Home Secretary, and the MI6 is to the Foreign Sectary.

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