The National Gallery and Tate Gallery Act 1954 is an Act of the Parliament of the United Kingdom (2 & 3 Eliz II c. 65). The Act came into force in 1955 and created a legal separation between the National Gallery and the Tate Gallery and established the Tate as an independent institution.
The Act was repealed on 1 September 1992 by the Museums and Galleries Act 1992, which created a board of trustees to operate the Tate.
References
National Gallery and Tate Gallery Act 1954 Wikipedia(Text) CC BY-SA