Editing MI5 (section)

{{Short description|British domestic intelligence agency}}
{{other uses|MI-5 (disambiguation)}}
{{distinguish|MI6}}
{{Use British English|date=March 2015}}{{Use dmy dates|date=April 2024}}
{{Infobox government agency
| name            = Security Service (MI5)
| type            = 
| seal            = 
| seal_width      = 
| seal_caption    = 
| seal_alt        = 
| logo            = Mi5 crest and logotype.svg
| logo_width      = 
| logo_caption    = 
| logo_alt        = 
| image           = Thames House and Lambeth Bridge, looking across the river.jpg
| image_size      = 275px
| image_caption   = [[Thames House]], London
| image_alt       = 
| formed          = {{Start date and age|1909|10|7|df=yes}}<br />(as the [[British Secret Service Bureau|Secret Service Bureau]])
| preceding1      = 
| jurisdiction    = [[His Majesty's Government]]
| headquarters    = [[Thames House]], [[London]], [[United Kingdom]]
| coordinates     = {{Coord|51|29|38|N|0|07|32|W|region:GB-WSM_scale:5000|display=title,inline|format=dms|name=Security Service – MI5}}
| motto           = ''Regnum Defende''<br />(Defend the Realm)
| employees       = 5,259<ref name="ISC_2021-2022">[https://isc.independent.gov.uk/wp-content/uploads/2022/12/ISC-Annual-Report-2021%E2%80%932022.pdf Intelligence and Security Committee of Parliament "Annual Report 2021–2022"]</ref>
| budget          = [[Single Intelligence Account]] £3.711 billion (2021–22)<ref name="ISC_2021-2022" />
| minister1_name  = [[Yvette Cooper]]
| minister1_pfo   = [[Secretary of State for the Home Department|Home Secretary]]
| minister2_name  = 
| minister2_pfo   = 
| chief1_name     = [[Ken McCallum]]
| chief1_position = [[Director General of MI5|Director General]]
| chief2_name     = 
| chief2_position = 
| parent_agency   = 
| child1_agency   = 
| child2_agency   = 
| website         = {{Official URL}}
}}
'''MI5''' ([[MI numbers|Military Intelligence, Section 5]]),<ref>{{Cite web |title=What's in a name? |url=https://www.MI5.gov.uk/home/about-us/who-we-are/mi5-history/whats-in-a-name.html |access-date=14 May 2014 |website=www.MI5.gov.uk |publisher=MI5}}</ref> officially the '''Security Service''', 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 (United Kingdom)|Joint Intelligence Committee]] (JIC), and the service is bound by the [[Security Service Act 1989]]. The service is directed to protect British parliamentary democracy and economic interests and to counter [[counter-terrorism|terrorism]] and [[counter-espionage|espionage]] within the [[United Kingdom]]. Within the civil service community, the service is colloquially known as ''Box'',<ref>{{cite web| url=https://www.telegraph.co.uk/news/uknews/crime/7969608/Annie-Machon-my-so-called-life-as-a-spy.html |archive-url=https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/news/uknews/crime/7969608/Annie-Machon-my-so-called-life-as-a-spy.html |archive-date=11 January 2022 |url-access=subscription |url-status=live|title=Annie Machon: my so called life as a spy|publisher=The Telegraph|date=29 August 2010|access-date=22 December 2020}}{{cbignore}}</ref> or  ''Box 500'',<ref>{{cite web|url=https://www.independent.co.uk/news/mi5-edges-out-of-the-shadows-42-of-elite-security-service-officers-are-women-terrorists-are-main-target-bugging-of-royal-family-denied-booklet-outlines-organisation-1485397.html|title=MI5 edges out of the shadows: 42% of elite Security Service officers are women – Terrorists are main target – Bugging of Royal Family denied – Booklet outlines organisation|work=The Independent|date=16 July 1993|access-date=22 December 2020}}</ref> after its official wartime address of PO Box 500; its current address is PO Box 3255, [[London]] SW1P 1AE.<ref>{{Cite book|title=The Irish War|first=Tony|last=Geraghty|location=London|publisher=HarperCollins|year=2000|isbn=978-0-00638-674-2}}</ref>

The Security Service is derived from the Secret Service Bureau, founded in 1909. At the start of the [[World War I|First World War]], it was responsible for the arrest of enemy spies, or suspected enemy spies. Throughout the First World War, Germany continually attempted to infiltrate Britain, but MI5 was able to identify most, if not all, of the agents dispatched. During the [[World War II|Second World War]], it developed the [[Double-Cross System]]. This involved attempting to 'turn' captured agents wherever possible, and use them to mislead enemy intelligence agencies.

After the war, the service was instrumental in breaking up a large [[Soviet Union|Soviet]] spy ring at the start of the 1970s. It then allegedly became involved in monitoring [[trade union]]s and left-wing politicians. It also assumed responsibility for the investigation of all [[Irish republicanism|Irish republican]] activity within Britain during [[The Troubles]]. Its role was then expanded to countering other forms of terrorism, particularly in more recent years the more widespread threat of [[Islamic extremism]]. In 1996, legislation formalised the extension of the Security Service's statutory remit to include supporting the law enforcement agencies in their work against serious crime.