The UK is a constitutional monarchy. The Head of State is the monarch (not a president), whose duties, functions and powers are conscribed by convention. One of the conventions is that the monarch is politically neutral.
England and Wales operate a common law system which combines the passing of legislation but also the creation of precedents through case law. The laws are established by the passing of legislation by Parliament which consists of the ‘Monarch’, the House of Commons and the House of Lords. The House of Commons is directly elected by the people and the Prime Minister is traditionally a member of this House. The Court System and case law are controlled by the judiciary which is completely separate to Parliament.
"All criminal cases will start in the Magistrates’ court, but more serious criminal matters are sent to the Crown Court. Appeals from the Crown Court will go to the Court of Appeal Criminal Division and potentially the UK Supreme Court.
Civil cases will usually start in the County Court. Again, appeals will go to the High Court and then to the Court of Appeal – although to different divisions of those courts. [And finally potentially the UK Supreme Court.]
The tribunals system has its own structure for dealing with cases and appeals, but decisions from different chambers of the Upper Tribunal, and the Employment Appeals Tribunal, may also go to the Court of Appeal.
The courts structure covers England and Wales; the tribunals system covers England, Wales and, in some cases, Northern Ireland and Scotland."
[Taken from https://www.judiciary.uk/about-the-judiciary/our-justice-system/court-structure/#:~:text=All%20criminal%20cases%20will%20start,start%20in%20the%20County%20Court. May 2024]
Books introducing the UK legal system can be found on Level 2, the entrance level to the library, with shelfmarks beginning KL11.
Unlocking the English Legal System by 
Introduction to the English Legal System by