Difference Between MI5 And MI6


MI5 and MI6 are military intelligence agencies that differ in their scope and objectives. Both are very important military agencies responsible for protecting the UK against potential threats. The main difference between the two is like the FBI and CIA in the USA – one is for domestic intelligence and one is for international intelligence.

Until 1991, MI5 and MI6 remained secrete organisations and nobody knew what exactly their roles were. At that time two also made public some previously classified information, such as the number of its employees and its organizational structure.

Let’s walk you through understanding MI5 and MI6 from their formation, cardinal responsibilities and how the two complement each other.

What is MI5?

The Security Service, also known as MI5 (Military Intelligence, Section 5) is the United Kingdom’s domestic counter-intelligence and security agency and is part of its intelligence machinery alongside the Secret Intelligence Service (MI6), Government Communications Headquarters (GCHQ), and Defence Intelligence (DI). MI5 is directed by the Joint Intelligence Committee (JIC), and the service is bound by the Security Service Act 1989.

In other words, MI5 is the intelligence agency charged with internal security and domestic counterintelligence activities of the United Kingdom. It is authorized to investigate any person or movement that might threaten the country’s security. Although MI5 is responsible for domestic counterespionage, it has no powers of arrest.

MI5 was formed in 1909 under the leadership of Vernon Kell, then a captain in the British army, to identify and counteract German spies then working in Britain, which it did with great effect. Kell retired as a major general in 1924 and was later knighted but remained in charge of the agency until 1940. (The name “MI5” originated during this period, when the agency was “section five” of military intelligence.)

What is MI6?

TheSecret Intelligence Service(SIS), commonly known as MI6 (Military Intelligence, Section 6), is the foreign intelligence service of the United Kingdom, tasked mainly with the covert overseas collection and analysis of human intelligence in support of the UK’s national security.

Formed in 1909 as the foreign section of theSecret Service Bureau, the section grew greatly during the First World War officially adopting its current name around 1920. The name “MI6” (meaning Military Intelligence, Section 6) originated as a convenient label during the Second World War, when SIS was known by many names. It is still commonly used today.

The existence of SIS was not officially acknowledged until 1994. That year the Intelligence Services Act 1994 (ISA) was introduced to Parliament, to place the organisation on a statutory footing for the first time. It provides the legal basis for its operations. Today, SIS is subject to public oversight by the Investigatory Powers Tribunal and the Intelligence and Security Committee of Parliament.

Since 1994, SIS headquarters have been in the SIS Building in London, on the South Bank of the River Thames. The stated priority roles of SIS are counter-terrorism, counter-proliferation, providing intelligence in support of cyber security, and supporting stability overseas to disrupt terrorism and other criminal activities. SIS works exclusively in foreign intelligence gathering; the ISA allows it to carry out operations only against persons outside the British Islands.


Key Difference

MI6, also known as the Secret Intelligence Service (SIS), is responsible for foreign intelligence and international espionage. It operates outside the UK’s borders and gathers intelligence from foreign sources to protect the UK’s interests and national security worldwide.

MI6’s main mission is to gather intelligence on foreign governments, organizations, and individuals that could potentially pose a threat to the UK or its allies.

MI6, historically, has had a more secretive profile. While its existence was acknowledged in the 1990s, much of its specific operations and activities remain confidential, and the identities of its agents are generally not disclosed.

MI5 (formally Security Service), is the intelligence agency charged with internal security and domestic counterintelligence activities of the United Kingdom. It is authorized to investigate any person or movement that might threaten the country’s security. Although MI5 is responsible for domestic counterespionage, it has no powers of arrest.

Other Differences

Legal Jurisdiction

  • MI5 operates under the Security Service Act of 1989 and has legal jurisdiction within the UK. Its operations are focused on countering domestic threats to national security.
  • MI6 operates under the Intelligence Services Act of 1994 and has a mandate for overseas intelligence operations. It gathers intelligence outside the UK’s borders to support national security and foreign policy.

Counterintelligence vs. Foreign Intelligence

  • MI5 specializes in counterintelligence, which involves identifying and neutralizing threats posed by foreign intelligence agencies and other hostile entities operating within the UK.
  • MI6 specializes in foreign intelligence gathering, which entails collecting information about foreign governments, organizations, and events to provide insight into international affairs.

Personnel and Recruitment

  • MI5 recruits individuals from within the UK, often seeking professionals with expertise in law enforcement, intelligence analysis and cybersecurity.
  • MI6 recruits individuals for intelligence operations in foreign countries. Its agents may come from various backgrounds and possess specialized skills such as languages, diplomacy, and international relations.

Operations and Activities

  • MI5’s operations involve counterterrorism, counterespionage, and counter-subversion activities. It investigates and monitors potential threats to national security within the UK.
  • MI6 engages in covert intelligence-gathering operations abroad, which may involve espionage, collecting information on foreign governments, and conducting secret missions to obtain critical information. Covert means may involve methods such as human intelligence (HUMINT) and signals intelligence (SIGINT) operations.

Leadership and Oversight

  • MI5 is overseen by the Home Office and is accountable to the UK government. Its Director General is a publicly known figure responsible for its overall operations.
  • MI6 is overseen by the Foreign and Commonwealth Office. Its Chief, often referred to as “C,” leads the agency and reports to the Foreign Secretary. The Chief’s identity is usually not publicly disclosed.

Target Audience

  • MI5’s audience is the UK government, providing intelligence and analysis to aid in making informed policy decisions to safeguard national security.
  • MI6’s audience is the UK government as well, but it provides intelligence on international matters, including geopolitical developments and foreign policy implications.

Domestic vs. International:

  • MI5 operates within the borders of the UK. Its activities involve monitoring and countering threats from individuals, groups, and organizations that pose risks to the nation’s security from within.
  • MI6 operates outside the UK’s borders and conducts intelligence operations in foreign countries. Its agents gather information about international events, foreign governments, and other global developments.

Public Profile

  • MI5 has a more visible public presence due to its involvement in counterterrorism and domestic security. It often collaborates with law enforcement agencies and engages with the public. In other words, MI5’s existence and some of its functions are publicly known.
  • MI6 historically had a more secretive profile. Its activities are generally more discreet and covert, with a stronger emphasis on operating in secret to gather foreign intelligence. Its activities are often classified and shrouded in secrecy.

Intelligence Sharing

  • MI5 collaborates closely with other domestic agencies, such as law enforcement and intelligence partners, to share information and address threats within the UK.
  • MI6 focuses on international intelligence sharing, cooperating with foreign intelligence agencies to exchange information on global security issues.