The UK spying agencies, the Security Service(MI5) and the Secret Intelligence Service(SIS or MI6) were founded in October 1909 as a single body known as the Secret Service Bureau, which was initially staffed by only 2 officers.MI5 was headed by an Army captain Vernon Kell and MI6 had the 50 - year - old Royal Navy Commander Mansfield Cumming as its chief, when the agencies soon grew to become professional spying apparatuses. Cumming and Kell later parted company to become the first heads of the future SIS(MI6) and MI5 respectively. MI5 played a key role in recognizing and capturing most of Germany’s spies in the UK at the beginning of World War One. At the outbreak of war in August 1914, the Anglo - German naval arms race created tensions between the two imperialist states and highlighted the need for them to adopt counter - espionage techniques in their attempts to defeat the other side of the conflict. Based at Thames House, London, the MI5 headed by Andrew Parker is responsible for protecting the UK, its citizens and interests, at home and overseas, against threats to national security. It’s answerable to Home Secretary. MI6, is headed by Sir John Sawers and it is responsible for gathering intelligence outside the UK in support of the government’s security, defence, foreign and economic policies. Based at Vauxhall Cross, London, the MI6 is answerable to Foreign Secretary. Known asThe Secret StateMI5 and MI6 operate as a ' state within a state ', having only token democratic accountability. They go to great lengths, including lying to elected ministers and use of the archaic ' Official Secrets Act ' to stave off embarrassing revelations about what a waste of British public money many of their operations are… and to deflect all scrutiny of their work. In the late 1970s and the early 1980s, MI5 enjoyed a very impressive agenda. Even, the British Broadcasting Corporations(BBC) allowed MI5 to investigate backgrounds and political affiliations of thousands of its employees, including reporters, newsreaders and continuity announcers. Confidential files, which shed light on the BBC’s hitherto secret links with the Security Service, show that at one stage it was responsible for vetting 6,300 different BBC posts, almost a third of the total workforce. The MI5 is usually concerned with domestic or internal security issues, but sometimes have overseas support on its missions. It can be compared to the well - known U. S. government agency, known as the FBI(Federal Bureau of Investigation). MI6, also referred to as the Secret Intelligence Service(SIS), is responsible for providing the British government with foreign intelligence. Its activities include a variety of secret political exploit triumphs, including the overthrow of Iran’s first democratically - elected government of late Mohammed Mossadeq in 1953(in collaboration with the U. S. Central Intelligence Agency). Britain’s spying apparatus MI6 has also been training, supporting and funding anti - Iran terrorist group - lets such as Jundallah headed by executed Abdolmalek Rigi, the Mojahedin - e Khalq Organization(MKO), the Kingdom Assembly, and PJAK, all of them have their offices based in London, according to documents even revealed by the British media outlets. Meanwhile, the assassination of some of Iran’s prominent nuclear scientists can be traced back to London. Two years before the start of the intelligence operations to sabotage Iran’s nuclear program, John Sawers, the head of MI6, talked about the ineffectiveness of U. S. - led sanctions imposed on Iran. A few weeks later, Iranian nuclear scientists including Majid Shahriari were assassinated. Moreover, some elements behind the 2009 sedition in Iran have turned up in Britain. MI6’s other operations include the joint overthrowing of Patrice Lumumba in the Congo, during the year 1961, and the commencement of an internal disagreement between Lebanese paramilitary groups in the second half of the 1980s, that successfully distracted them from further captive takings of Westerners in the area. This branch of the British government is comparable to the United States’ CIA(Central Intelligence Agency). From among prominent people working with the British spying agencies, reports had it that David Kelly was an MI6 agent who was murdered and that former prime minister Tony Blair worked as a spy for MI5 before he became Labour Party’s chief. And finally, although MI5 and MI6 are the famous departments that everybody knows of, other ‘MI’ departments are also supposed to have existed, albeit not necessarily known by the MI prefix, and many not confirmed by the Ministry of Defence(MoD). During the First World War, British secret services were divided into numbered sections namedMilitary Intelligence, department number x, abbreviated to Mix, such as MI1 for information management. The branch, department, section, and sub-section numbers varied through the life of the department, the examples of which are as follows: MI1 known as government’s communication headquarters whose concern was codes & ciphers MI2 was concerned with issues of the Middle and Far East, Scandinavia and USSR MI3 was responsible for Germany and Eastern Europe MI4 was responsible for aerial reconnaissance MI5 is tasked with domestic spying and counterintelligence MI6 works as a liaison with Secret Intelligence Service and Foreign Office MI7 was tasked as ‘press and propaganda’ outlet MI8 was responsible for signals interception and communications security MI9 worked as a mechanism for Clandestine Operations, Escape and Evasion MI10 Weapons and Technical Analysis MI11 Field Security and Police MI12 was tasked with military censorship MI13 there was no such a thing except in fiction MI14 Germany and German-occupied territories MI15 whose main task was aerial photography MI16 was responsible for scientific spying MI17 was the secretariat for Director of Military Intelligence MI18 was used only in fiction MI19 was responsible for interrogating Prisoners of Wars (PoWs) The information provided in the above list has been exposed thanks to Freedom of Information Act. However, it is classified and may never be fully released, and the extent to which that list is accurate is unknown. Many MI departments, might, for instance, still exist alongside the ones we know about. However, many more may have existed and now be defunct.