Constitutional law is the law that deals with making laws, thereby governing the hierarchies and relations between the judiciary, legislature and executive. The 3 different powers of judiciary, legislature and executive, are as a result of the separation of powers.
Whereas the United Kingdom is a unitary state, United States and Australia is a federal state. Whereas with unitary states, the delegated powers can be taken back; with federal states, the delegated powers are set in print in the constitution, and therefore cannot be altered (unless the constitution is changed, which is essentially impracticable, if not impossible).
Because constitutional law governs the making of laws, it has the ability to override law, created by parliament. As a result, constitutional law is particularly powerful as human rights.
In particular, in jurisdictions like the United States and France that have a bill of rights, all laws are required to abide with the bill of rights, which state basic political, social and economic standards that all laws must meet.