Short answers, pulled from the story.
The Alkali Act 1863 was passed to curb the discharge of muriatic acid gas, which is gaseous hydrochloric acid, from Leblanc alkali works into the air. It created an alkali inspector and four sub-inspectors to enforce this control. The act was later extended to cover other industrial pollutants beyond muriatic acid gas.
Dr Robert Angus Smith was the first Chief Inspector, a position created by the Alkali Act (1863) Amendment Act 1874. He was statutorily responsible for the standards set and maintained by the Inspectorate and reported directly to the Permanent Secretary of his department.
The Alkali Act 1863 was made permanent by the act 31 and 32 Vict. c. 36, sometimes called the Alkali Act 1868, which removed the original expiry date of the 1st of July 1868 and continued the act without any such limitation.
The Alkali Acts were finally replaced by the Environmental Protection Act 1990. Before that, the 1863 act had been repealed by the Alkali, and Works Regulation Act 1881, which was itself later superseded by subsequent versions in 1892 and 1906.
The inspectorate worked under several departments across its history: the Board of Trade from 1863 to 1872, the Local Government Board from 1873 to 1918, the Ministry of Health from 1919 to 1951, the Ministry of Housing and Local Government from 1951 to 1970, and the Department of the Environment from 1970 to 1975. It was then transferred to the Health and Safety Executive in 1975, which ended the Chief Inspector's independence.
Her Majesty's Inspectorate of Pollution, known as HMIP, was the name given to the inspectorate when it was transferred back to the Department of the Environment in 1987. It had previously operated as the Industrial Air Pollution Inspectorate from 1983 to 1987, and it descended directly from the inspectorate created by the Alkali Act 1863. HMIP became part of the Environment Agency and Scottish Environment Protection Agency on the 1st of April 1996.