There is information on statute in section 10.16 of the Concise Guide, (p. 361 of the Publication Manual) but it is US focused, and UK universities each offer slightly differing guidance. We recommend treating Acts of Parliament similarly to a website.
In text citation:
Parenthetical: (Data Protection Act 2018)
Narrative: Data Protection Act 2018
Note that the year is part of the Act title, so it is not separated from the rest.