Question: John le Carré worked for a UK service bound by what?

Context paragraphs:
Bill Haydon: Bill Haydon is a fictional character created by John le Carré in le Carré's "Tinker Tailor Soldier Spy".

Control (fictional character): Control is a fictional character created by John le Carré.  Control is an intelligence officer who acts as the head of "the Circus", the British overseas intelligence agency.  He is a character in the novels "The Spy Who Came in from the Cold", "The Looking Glass War", and "Tinker Tailor Soldier Spy", and is referred to in several others, usually by association with le Carré's recurring protagonist George Smiley, who has served as Control's right-hand man.

Joseph Hone: Joseph Hone (February 25, 1937 – August 15, 2016) was an Irish writer of the spy novel.  His most famous novels featured a British spy called Peter Marlow.  The first of the series was "The Private Sector" (1971), set in the Six Day War.  Marlow's story continues in "The Sixth Directorate" (1975), "The Flowers of the Forest" (a.k.a. "The Oxford Gambit") (1980), and "The Valley of the Fox" (1982).  During his heyday, in the 1970s, Hone was favourably compared with writers such as Len Deighton, Eric Ambler and John le Carré.  Whilst some spy novels, such as those of le Carré are often set mainly inside the offices of the spy department, and attract praise for the depth of their characterization and plotting, others (such as the James Bond series) are set in the field, and provide explosive action.  Joseph Hone's stories by contrast, have a foot in both camps, and he has become renowned amongst aficionados of the spy genre for both the quality of his writing, and the excitement of his plots.  He released his memoir, "Wicked Little Joe" in 2009.

Connie Sachs: Connie Sachs is a fictional character created by John le Carré.  Sachs plays a key supporting role in le Carré's "Karla Trilogy" of spy novels including "Tinker Tailor Soldier Spy"; "The Honourable Schoolboy"; and "Smiley's People".

Call for the Dead: Call for the Dead is John le Carré's first novel, published in 1961.  It introduces George Smiley, the most famous of le Carré's recurring characters, in a story about East German spies inside Great Britain.  It also introduces a fictional version of British Intelligence, called "the Circus" because of its location in Cambridge Circus, that is apparently based on MI6 and that recurs throughout le Carré's spy novels.

John le Carré: The Biography: John le Carré: The Biography is a 2015 biography of John le Carré written by Adam Sisman and published by Harper.

The Deadly Affair: The Deadly Affair is a 1966 British espionage–thriller film, based on John le Carré's first novel "Call for the Dead".  The film stars James Mason, Harry Andrews, Simone Signoret and Maximilian Schell and was directed by Sidney Lumet from a script by Paul Dehn.  In it George Smiley, the central character of the novel and many other le Carré books, is renamed Charles Dobbs as Paramount, which owned the film rights of their recently filmed "The Spy Who Came in from the Cold", had the rights to the Smiley character.  The soundtrack was composed by Quincy Jones, and the bossa nova theme song, "Who Needs Forever", is performed by Astrud Gilberto.

Spy film: The spy film genre deals with the subject of fictional espionage, either in a realistic way (such as the adaptations of John le Carré) or as a basis for fantasy (such as many James Bond films).  Many novels in the spy fiction genre have been adapted as films, including works by John Buchan, le Carré, Ian Fleming (Bond) and Len Deighton.  It is a significant aspect of British cinema, with leading British directors such as Alfred Hitchcock and Carol Reed making notable contributions and many films set in the British Secret Service.

MI5: The Security Service, also 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.  The service is directed to protect British parliamentary democracy and economic interests, and counter terrorism and espionage within the UK.

John le Carré: David John Moore Cornwell (born 19 October 1931), known by the pseudonym John le Carré ( ), is a British author of espionage novels.  During the 1950s and the 1960s, he worked for both the Security Service and the Secret Intelligence Service, and began writing novels under his pen name.  His third novel, "The Spy Who Came in from the Cold" (1963), became an international best-seller and remains one of his best-known works.  Following the success of this novel, he left MI6 to become a full-time author.

Supporting paragraphs: John le Carré MI5
Answer: Security Service Act 1989