"Great Britain" means England, Wales, Scotland, their adjacent territorial waters and the islands of Orkney and Shetland, the Hebrides and, by virtue of the Island of Rockall Act 1972, Rockall.
This became the usual way to refer to Acts in the second half of the 19th century, starting in the 1840s; previously Acts were referred to by their long title together with the regnal year of the parliamentary session in which they received Royal Assent, and the chapter number.