For common law countries, it is generally true that procedural rules take precedence over substantive criminal rules. But whereas in England the rules of criminal procedure were based on statute, in the United States criminal procedure was a “constitutional matter”, a fundamental element of federal common law. A significant difference in procedural guarantees is that English guarantees are based on statutes and estates and can be changed by regulation, whereas US guarantees can only be changed by constitutional amendment, possibly by a Supreme Court decision.