Constitutions, or charters, are documents which set forth the structure and rules of governance. These entities ruled by constitutions can be countries or "artificial persons" (that is corporations, trusts, Companies, Unincorporated institutions, Partnerships, and so on).
That said, the US Constitution is a separate thing from the British Constution. Well, the British Constution isn't really a document, but a set of laws. That is constitutional statutes enacted by the Parliament (E.G, House of Commons Disqualification Act 1975, Northern Ireland Act 1998, Scotland Act 1998, Government of Wales Act 1998, European Communities Act 1972 and Human Rights Act 1998) and also unwritten sources such as constitutional conventions, observation of precedents, royal prerogatives, custom and tradition, such as always holding the General Election on Thursdays.
There is no difference in legal terms between constitutional law and statutory law (i.e. law applying to any area of governance) in the English system. Both can be altered or repealed by a simple majority in Parliament. In practice, democratic governments do not use this opportunity to abolish all civil rights, which in theory they could do, but the distinction between regular and constitutional law is still somewhat arbitrary, usually depending on the traditional devotion of popular opinion to historical principles embodied in important past legislation. For example, several Acts of Parliament such as the Bill of Rights, Human Rights Act and, prior to the creation of Parliament, Magna Carta are regarded as granting fundamental rights and principles which are treated as almost constitutional.
By separating itself from England, The United States broke with English Constitutional law and created its own rules of governance. The law of the United States was originally largely derived from the common law system of English law, which was in force at the time of the Revolutionary War. The supreme law of the land, under the Constitution's Supremacy Clause (VI), is the United States Constitution, as well as laws enacted by Congress, and treaties to which the U.S. is a party. The Constitution forms the basis for federal laws under the federal constitution in the United States; it circumscribes the boundaries of the jurisdiction of federal law along with the laws in the fifty U.S. states and in the territories.
The most important source of law is the United States Constitution. All other law falls under and is subordinate to that document. No law may contradict the Constitution. For example, if Congress enacts a statute that conflicts with the Constitution, the Supreme Court may find that law unconstitutional and declare it invalid. Notably, a statute does not disappear automatically merely because it has been found unconstitutional; it must be deleted by a subsequent statute. Many federal and state statutes have remained on the books for decades after they were ruled to be unconstitutional. However, under the principle of stare decisis, no sensible lower court* will enforce an unconstitutional statute, and any court that does so will be reversed by the Supreme Court. Conversely, any court that refuses to enforce a constitutional statute (where such constitutionality has been expressly established in prior cases) will risk reversal by the Supreme Court. (But who reverses the ninnies when they mess up???)
While Blackstone may have talked about rights, he knew full well they could be repealed by Parliament. This is why the language is "bear arms for their own defense, as suitable to their class and as allowed by law". This is the way rights are treated under the English Constitution. Here today and gone tomorrow.
Again, if one uses Blackstone as a source, one knows that the right to bear arms for defence in England (and by extension the UK and other common law countries) is next to nil as well. This is because the right is "as allowed by law". That is it is under regulation by parliament and not as absolute as the language in the Second Amendment. The Founding fathers were well aware of the tenuous nature of rights under the English system, which did not define or quantify natural rights. They believed that adding a Bill of Rights to the Constitution would limit their rights to those listed in the Constitution. This is the primary reason the Ninth Amendment was included.
On June 5, 1788, Patrick Henry spoke before Virginia's ratification convention in opposition to the Constitution: "Is it necessary for your liberty that you should abandon those great rights by the adoption of this system? Is the relinquishment of the trial by jury and the liberty of the press necessary for your liberty? Will the abandonment of your most sacred rights tend to the security of your liberty? Liberty, the greatest of all earthly blessings—give us that precious jewel, and you may take every thing else!"
The founders knew they were setting up a totally new and different system from the English one under the US Constitution.
Of course, as I read more about Scalia's pretensions at "originalism", the more I worry that he is willing to destroy rights willy nilly in the common law fashion. Sod the fact the US Constitution is a written document: he'll tear it up.
But, I would prefer for my elected officials to do that. There is a reason that Royalty and nobility are unconstitutional.
Unless, of course, I am calling the shots here!
* On the other hand, a non-sensical supreme court can do whatever it wishes until whapped over the head.