| Sir Robert Anderson | Assistant Commissioner in charge of CID, Metropolitan Police 1888–1901. Engaged by Home Office on secret Irish work 1868; ran entrapment operations against Irish Nationalists. |
| Arthur Balfour | Nephew of Lord Salisbury, Conservative MP 1874–22. Prime Minister (1902–05), Foreign Secretary 1916–19). |
| Sir Edward Bradford | Chief Commissioner, Metropolitan Police, from 1890 following the resignation of James Monro. |
| William Burrell | Divisional Detective Inspector, CID, Metropolitan Police, from 1888. Special Staff, MI5, from 1914. |
| Vladimir Burtsev | Russian Revolutionary journalist and émigré. Arrested and tried for incitement to murder the Tsar in 1898. |
| Hector Bywater | Agent, Secret Service Bureau, from 1910. |
| Auguste Coulon | French anarchist and police informer. Suspected agent provocateur in 1891 Walsall bomb case. |
| Sir Henry Curtis-Bennett | Barrister; defence counsel at German espionage trials in First World War. Agent, MI5, from 1916. |
| Sir Mansfield Cumming | Head of Foreign Department, Secret Service Bureau, from 1909. Director of Secret Intelligence-Service (MI6) until 1923. |
| Major James Edmonds | Head of Section H, Intelligence Department, War Office, from outbreak of Boer War. Head of special section, Directorate of Military Operation. Led initiative resulting in creation of Secret Service Bureau, October 1909. |
| Herbert Fitch | Inspector, Special Branch. Resigned from Metropolitan Police January 1924. |
| Major Nicholas Gosselin | Deputy to Edward Jenkinson, Assistant Under-Secretary, Police and Crime in Ireland, from 1884. |
| Arthur Hailstone | Inspector, Special Branch, Metropolitan Police, from 1891. Secret Service Bureau from 1911. |
| Sir William Harcourt | Anti-imperialist Liberal MP 1868– 1904. Home Secretary (1880–85). |
| Sir Edward Henry | Assistant Commissioner in charge of the CID, Metropolitan Police (May 1901–March 1903). Chief Commissioner (1903–18). |
| Edward Jenkinson | Pro-Home Ruler; Assistant Under-Secretary, police and crime in Ireland, from 1882. Recruited own spy ring and adopted covert role at Home Office. |
| Sir Vernon Kell | German intelligence analyst, War Office from 1902. Head of Home Department, Secret Service Bureau, from 1909. Director General, MI5, until 1940. |
| William Knox D’Arcy | Solicitor who purchased concession to prospect for oil in Persia 1901. Secured backing of British Government and Burmah Oil 1905, struck oil 1908 to form company now known as BP. |
| Chf. Inspector John Littlechild | Inspector, Special Irish Branch. Head of Special Branch (1887–1903). |
| Henry Dale Long | Agent, ‘W. Morgan Investigation Bureau’, from 1903. Secret Service Bureau from 1909. |
| Sir Melville MacNaghten | Assistant Commissioner in charge of CID, 1903–13. |
| Sir Henry Matthews | Home Secretary 1886–90. Attracted severe criticism over failure to apprehend Jack the Ripper. |
| Det. Sergeant Patrick McIntyre | Founder member, Special Irish Branch, 1882. Head of Special Branch; reduced to ranks after disciplinary action. |
| General F. F. Millen | Double agent. Member, Fenian Brotherhood and Clan-na-Gael; took part in unsuccessful Irish coup 1865. Named by James Monro as instigator of 1887 Jubilee Plot. |
| James Monro | Assistant Commissioner in charge of CID, Metropolitan Police, 1884–88. Chief Commissioner until 1890. |
| Joseph Moroney | Alias: Joseph Melville. Member, Clan-na-Gael. Involved in 1887 Jubilee Plot. |
| Charles Parnell | Irish Nationalist MP 1875–90; Irish Leader, House of Commons 1878. Political career ruined by divorce case. |
| Jacob Peters | Latvian revolutionary arrested for murder after Houndsditch shootings. member, Bolshevik Party; Deputy Chairman, Cheka, from 1917. |
| Patrick Quinn | Founder member, Special Irish Branch. Superintendent and Head of Special Branch 1903–18. |
| Sidney Reilly | Born Sigmund Rosenblum. Special Branch informer from 1896. Agent, Secret Intelligence Service (1918–22); executed by Russian secret police 1925. |
| Gustav Steinhauer | Chief of German Secret Service; established spy network in Britain before First World War. Bodyguard to Kaiser, worked with Melville, to thwart assassination attempt on Wilhelm II. |
| Richard Tinsley | Agent, Secret Service Bureau; provided intelligence on suspected German spies heading for Britain via Belgium. |
| Sir James Trotter | Head of Secret Section 13, War Office. Recruited Melville 1903 to take responsibility for agent recruitment and co-ordination. |
| Howard Vincent | Founder and first Head of Criminal Investigation Department, Metropolitan Police. Assistant Commissioner in charge of CID 1878–84. |
| Sir Charles Warren | Chief Commissioner, Metropolitan Police 1886–88; resigned in wake of police failure to apprehend ‘Jack the Ripper’. |
| Adolphus ‘Dolly’ Williamson | First Head of Detective Department and Head of Special Irish Branch 1882–87. Deputy to James Monro from 1887. |