1962: 10 & 11 Eliz. 2 c.34: An Act to provide for the numbering and citation of future Acts of Parliament by reference to the calendar year in which they are passed.
[19th July, 1962.]
BE it enacted by the Queen’s most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows:—
[Numbering and citation of future Acts.]
1. The chapter numbers assigned to Acts of Parliament passed Numbering in the year nineteen hundred and sixty-three and every subsequent year shall be assigned by reference to the calendar year, and not the Session, in which they are passed; and any such Act may, in any Act, instrument or document, be cited accordingly.
2. This Act may be cited as the Acts of Parliament Numbering and Citation Act, 1962.
Source: Public General Acts 1962.
Further reading: Wikipedia.