Once a court has set precedent, can it ever be ignored? Is it legally binding, or just very persuasive advice? Are there any examples of a judge ignoring precedent without setting new precedent, or is that paradoxical?
Precedent in common law is based on a hierarchy of courts. This is the hierarchy in the UK: as they say, it's complicated because it represents 1,000+ years of organic growth rather than a system that was planned.
Precedent is binding on courts lower in the hierarchy than the one who set the precedent. If a judge ignores a precedent (that was argued by one side or the other1) then the decision is wrong and would be overturned on appeal.
Precedent at the same level and in parallel jurisdictions is persuasive, if a judge ignores it they better have good reason for doing so (and put those reasons in the judgement) or they will probably have their decision overturned on appeal. A parallel jurisdiction is a common law jurisdiction in another country like Australia, Canada or (rarely) the USA. It is quite common for parliament when drafting new laws to look at similar laws in other jurisdictions as a starting point. When cases are brought under such new legislation it is right that precedent set on similar law in other jurisdictions serves as the starting point for case law in the U.K.
Precedent turns on the law and the facts involved. If parliament changes the law then many precedents may be invalidated. Similarly, the facts of cases are never exactly the same, argument in court is often not about the facts - these may be agreed - but about why these facts are the same/different so that this precedent should/should not apply.
Incidentally, precedent is one of the main differences between common law (English) and civil law (European) legal systems: common law has it, civil law doesn't.
- A judge must decide the case that is argued before them, deciding on a basis that the parties didn't argue is a breach of natural justice: if both sides fail to raise an applicable precedent then it is not something the judge should consider. A judge who is aware of a precedent that neither side has raised it should draw it to their attention so they can argue it.