Legal proceedings in England are largely a contest between opposing parties (prosecution/plaintiff and defense) with a judge acting as a neutral moderator rather than conducting the investigation.
The UK does not have a single codified document. It relies on a combination of statutory law, common law, and conventions. Law Express. English Legal System
Here is an analysis of this feature and others covered in the Law Express series: Legal proceedings in England are largely a contest
The justice system and the constitution - Courts and Tribunals Judiciary ensuring consistency and predictability.
The system relies heavily on judicial decisions from past cases (case law) rather than just written codes. Higher courts bind lower courts, ensuring consistency and predictability.