The United Kingdom Immigration Service, (previously known from 1920 to 1933 as the Aliens Branch and from 1933 to 1973 as the Immigration Branch), was the operational arm of the Home Office, Immigration and Nationality Directorate. The UK Immigration Service was, until its disbandment in 2007, responsible for the day-to-day operation of front line UK Border Controls at 57 ports "designated" under the Immigration Act 1971 including airports, seaports, the UK land-border with Ireland and the Channel Tunnel juxtaposed controls. Its in-country enforcement arm was responsible for the detection and removal of immigration offenders such as illegal entrants, illegal workers and overstayers as well as prosecutions for associated offences. On its disbandment, Immigration Service staff were re-deployed within the short lived Border and Immigration Agency which was replaced by the UK Border Agency which, in turn, was replaced by three separate entities UK Visas and Immigration, Border Force and Immigration Enforcement. All three overseen by Home Office.