Firstly you have to understand the Separation of Powers Act. This sets a a constitutional basis from which the law functions. The Judiciary - The legislative - The Executive. This defines that the individual is secure only if these three primary functions of the state are exercised independently
The establishing of laws is done in varying ways.
(1) The Executive or The Government form laws in the House of Commons by setting out Bills. This may have come from their election mandate for example > The Labour Party state - if you elect us we will ban Fox Hunting ? They are elected so when in parliament they set out a Bill to become an ACT which is passed through the house and then to the House of Lords as a checking procedure. If the H o L vote against it the Executive ( because they were elected by the people) can ignore the house of lords and pass the Act. Thus Fox Hunting is illegal.
(2) Statutory Instrument. - This is when the minister, lets say the Minister overseeing Fox Hunting or the Hunting of animals in general > can enact or remove part of the composite law EG > When the law on fox hunting was passed it may have included within its written form clauses whereby the Minister can make a decision without having a full debate or vote in the house. So he may say "I will allow Fox Hunting on Saturdays only on one day per year" ( silly but the point is evident) but his power to do this must have been permitted in the first draft within the act therefore he is acting legally and not as a dictator.
(3) Case made Law - This is when the court of appeal acts on a decision made by a lower court and in doing so establishes it in law. But the judges can only operate within the statute / Act set by parliament. another example - Judicial Review ( a hearing in front of a judge on administrative matters to ensure that public officers - prison staff - police - Benefits office - and the like do not operate beyond their powers) A true case > years ago prisoners who were refused parole were NOT told the reason why, four prisoners took their case to Judicial Review stating it was unfair and that the Prison Service were acting beyond their powers. The judge upheld their case, thereafter the Prison Service had to give reasons to all prisoners. This was now law.
(4) The House of Lords only deals with Appeals which are a point of law but once they rule their decision becomes law.
(5) Bye Laws - laws when say a local Council rule on a matter - yellow lines - pubs closing etc.
The main point is NO ONE PERSON OR BODY can be a dictator they can only operate within the Act of parliament or Statute Law.
So when a man is convicted of Murder the Judge MUST give him a LIFE SENTENCE, he has no choice - even if he thinks the man was of good standing with no previous convictions, the judge can not give him any other sentence - say 3 years in prison ? he must give him a life sentence. Because the statute law (passed in parliament) states this. equally the man cannot appeal against sentence he can only appeal against conviction because there is no other sentence available for a murder conviction.
A long answer but I hope it helps a little.
PS > Recently a man took the government to court in regard of the election system via Judicial Review - his claim was that when a party stands for election and is voted on their mandate, win and become the government, then they must carry out all of that mandate because that was why they were elected. The Judge DID NOT RULE IN HIS FAVOUR, therefore an elected party does not have to follow its mandate . IN SHORT - WHATS THE POINT ???