Lawyers often assume that non-lawyers understand how our laws come about, but there is no more reason why they should than I should know how a nurse sutures a wound, or the talented guy at PC World fixes my computer.
So, in one paragraph I am going to tell you. It is, essentially, a mix of ‘common law’ principles, evolved over the centuries by judges, of various hues, and statutes passed by Parliament. The common law principles are developed and refined in case law i.e. literally, on a ‘case by case’ basis, as is the interpretation of statute law. The EU has added an extra dimension in the mix as EU law can (sometimes) be directly enforceable in the UK.
Case law is otherwise known as precedent. In a law degree and in law school, aspiring lawyers learn lots of precedents, some of which are more memorable than others, depending on the factual basis. One case all law students remember for instance is Donoghue v Stevenson not only because it is a key case in establishing principles of the law of negligence but because it is all about someone finding a dead snail in a ginger beer bottle and what to do about that. Less memorable cases are ones with boring facts and/or about very difficult abstruse points of law and with names that are very long and difficult to remember such as Mulugeta Guadie Mengiste and Other v Endowment Fund for the Rehabilitation of Tigray and Others (one I just came across recently in the reports)
Law firms incidentally can have memorable and less memorable names too. I think ours is easy enough to recall, but Ziffren, Brittenham, Branca, Fischer, Gilbert-Lurie, Stiffelman, Cook, Johnson, Lande & Wolf, isn’t.