UK legislation falls into two general types: Acts of Parliament or statutes, and delegated (or secondary) legislation, called statutory instruments (SIs), which can make detailed changes to the law.
There are various sources of UK legislation, including statutes and statutory instruments. Subscription databases, such as LexisLibrary and Westlaw UK carry the full text of legislation, whereas JustCite indexes statutory provision, but does not carry the full text.
Both LexisLibrary & WestLaw UK carry amended legislation, taking into account any amendments to statutes and SIs, or repeals of sections or subsections.
WestLaw UK also carries historical versions of legislation, showing you as it was before amendments /repeal.
Use Halsbury's: Is it in force? (via LexisLibrary) to tell if an act, or section of an act is currently in force. (Note some acts don't come into force until some time after they are given royal assent.)