The doctrine of implied repeal is a concept in constitutional theory which states that where an Act of Parliament or an Act of Congress conflicts with an earlier one, the later Act takes precedence and the conflicting parts of the earlier Act are repealed (i.e., no longer law). This doctrine is expressed in the Latin phrase "leges posteriores priores contrarias abrogant".
Express repeal is carried out by judges in the same method as above, however, Parliament or Congress expressly orders judges to allow a statute to prevail over a previous statute.[clarification needed]
Under United States law, "implied repeal" is a disfavored doctrine. That is, if a court can reconcile the two statutes with any reasonable interpretation, that interpretation is favorable to one that deems the earlier statute to have been invalidated by the later one.
Constitutional statutes in the United Kingdom: not subject to implied repeal
In the 2002 English case Thoburn v Sunderland City Council (the so-called 'Metric Martyrs' case), Lord Justice Laws ruled that some constitutionally significant statutes held a higher status in UK law and were not subject to the doctrine of implied repeal and would therefore require Parliament to expressly repeal the Act. The case specifically dealt with s.2(2) of the European Communities Act, but in his judgment, Lord Justice Laws also named the Parliament Act and the Human Rights Act as other 'constitutional statutes' and therefore not subject to the doctrine. Constitutional statutes can still be expressly repealed if Parliament wishes, but unless the words doing so are totally unambiguous, the courts will follow the precedent established in Thoburn.
A decade later in 2012, in a case before the Supreme Court of the United Kingdom, BH v The Lord Advocate (Scotland), Lord Hope said in paragraph  of the judgment to the effect that “the Scotland Act can only be expressly repealed; it cannot be impliedly repealed; that is because of its ‘fundamental constitutional nature’.”
- Free Life Commentary No 63
- See Stop Youth Addiction, Inc. v. Lucky Stores, Inc., 950 P.2d 1086, 1096 (Cal. 1998) (recalling that to overcome the strong presumption against implicit repeal the two provisions must be so inconsistent that they cannot have concurrent operation).
-  UKSC 24
- Adam Perry and Farrah Ahmed: Are Constitutional Statutes ‘Quasi-Entrenched’? Blog of the UK Constitutional Law Association