Common law and statute law: the hierarchy of law-making
English and Welsh law is made up of common law and statute law – what I shall call, together, primary law; and, of the two, statute law will always trump common law. Common law is made for the most part by judges of the High Court, Upper Tribunal, Court of Appeal and Supreme Court. Statute law is made by Parliament (strictly speaking by the queen in Parliament).
Many modern statutes, of necessity, delegate law-making to government departments or to other statutory bodies. These bodies are then responsible for making subsidiary (or delegated) legislation, subject only to parliamentary approval. Much of the legal aid scheme depends on various levels of subsidiary legislation, as does the child support scheme; and family law could not work without Family Procedure Rules 2010 which are delegated to Family Procedure Rules Committee by Courts Act 2003 ss 75 and 76.
Subsidiary to this delegated legislation, and not even subject to direct parliamentary approval, are certain murky powers – some statutory and some less so – to issue guidance and make practice directions. Thus under Legal Aid Sentencing and Punishment of Offenders Act 2012 s 4 the Lord Chancellor has be given power by Parliament to issue guidance as to the operation of the exceptional case funding provisions of LASPOA s10. President of Family Division is able (nominally with the approval of the Lord Chief Justice) to issue practice directions for the guidance of litigants in family proceedings; and Family Procedure Rules Committee (see below) has powers to make such directions also.
The Lord Chancellor’s guidance on exceptional case funding (https://www.gov.uk/government/publications/legal-aid-exceptional-case-funding-form-and-guidance) has been twice successfully shown in certain important respects to be unlawful (R (ota Gudanaviciene & Ors) v The Director of Legal Aid Casework & Ors  EWCA Civ 1622; and again in IS v The Director of Legal Aid Casework & Anor  EWHC 1965 (Admin), Collins J). Twice this year already practice directions have been shown by Supreme Court to be outside the powers – ultra vires – the body with power to make them; and Family Procedure Rules Committee have consigned most aspects of care proceedings in a way which is of such detail and which avoids legitimate statutory or delegated legislation, such that it is, in many respects, of dubious lawfulness. (Children lawyers are such a supine bunch that they do not trouble to take the Lord Chancellor or FPRC (his committee) to task for this).
Subsidiary legislation: within bounds defined by Parliament
The critical feature of all this is to appreciate that delegated legislation can only exist, lawfully, if it comes within the bounds defined by Parliament; and, as Collins J explained in IS, guidance – even more so – must come within the intent of the statutory scheme as set out by Parliament (that is the point of democratic direction to ministers: and see Padfield v Minister of Agriculture, Fisheries and Food  AC 997).
And thus the law comes full circle. Judge-made common law comes back into play to explain what a particular statutory provision means (including delegated legislation and guidance, as with the Gudanaviciene and IS cases); or to say that subsidiary legislation is not within the powers delegated by Parliament.
An excellent example of the creation of law by the judges is the Gillick case. Family Law Reform Act 1969 s 8 says that a child over 16 can consent to medical treatment as if the ‘child were an adult’; but under that age the question of a child’s consent depends on their age and understanding as defined or explained by Gillick v West Norfolk and Wisbech AHA  1 AC 112,  UKHL 7,  1 FLR 224. The first period – 16-17 is entirely statutory; but to understand the rights of a child up to his/her sixteenth birthday we are dependent entirely on the common law.
As Lord Scarman explained it:
The law has, therefore, to be found by a search in the judge-made law for the true principle. The legal difficulty is that in our search we find ourselves in a field of medical practice where parental right and a doctor’s duty may point us in different directions. This is not surprising. Three features have emerged in today’s society which were not known to our predecessors: (1) contraception as a subject for medical advice and treatment; (2) the increasing independence of young people; and (3) the changed status of woman. In times past contraception was rarely a matter for the doctor:…, women have obtained by the availability of the pill a choice of life-style with a degree of independence and of opportunity undreamed of until this generation and greater, I would add, than any law of equal opportunity could by itself effect.
And thus is a balance held and a symbiosis maintained: first is the common law, save where – secondly – the law is developed, altered or codified by Parliament. Subsidiary to statute law are the forests of delegated legislation and guidance. And then, finally, the judge’s sweep up: watching over laws set out by Parliament and searching out Lord Scarman’s ‘true principle’ where none has yet been defined.