The primary sources of law are legislation and case law, these are the most authoritative sources of legal information.
Legislation
In Skills for Law Students on page 490, the glossary describes 'legislation' as being:
"The whole or any part of a country's written law, usually used to mean Acts of Parliament or Statutes, but also including delegated or secondary legislation."
You may also see the terms delegated or secondary legislation described as 'subordinate legislation' or 'statutory instruments'.
Cases
In Skills for Law Students on page 485, the glossary describes cases as:
"... the arguments put forward by both sides of a court action, as well as the report of the judicial decision."
Law Reports
In Skills for Law Students on page 490, the glossary describes law reports as:
"Reports of decisions handed down by the courts. Since 1865 these have mainly been handled by the Incorporated Council of Law Reporting, which publishes The Law Reports - reports of cases selected by the Council for their importance, written by lawyers and approved by the judges presiding. Further to the Council, there are other commercially published reports, e.g. the All England Law Reports."
There are many cases heard each day, the most important decisions are heard in the Superior and Appellate Courts of England and Wales and are observed by court reporters. These observations are written up as case law reports which are later made available in the legal databases and are published in printed volumes and made available in libraries. There are many series of law reports available, some contain reports from a range of legal practice areas, others are specific to a single area e.g. the Family Law Reports, Entertainment and Media Law Reports etc.
Authority of Law Reports
The most authoritative series of law reports are published by the Incorporated Council of Law Reporting (the ICLR). This series is known as The Law Reports and contains reports from Appeal Cases (AP), Queen's Bench (QB), Chancery (Ch) and Family (Fam). This series is deemed most authoritative by the judiciary as the reports contain a detailed summary of the legal arguments checked by the bench before publication. If a report of the case you are reading is available from this series you should cite it in preferance to any other as decreed in the Practice Direction: Citation of Authorities (2012).
If a judgment is not or not yet published in The Law Reports then cite a report from either the Weekly Law Reports (WLR) or the All England Law Reports (All ER). If the judgment is not available from any of these series then cite a report from one of the authoritative specialist series.