There are so many inaccuracies here.
The Duke of Cambridge is not the Head of State; he's the Head of State's grandson.
The UK does have a constitution; it just doesn't have one which is written down in one place.
The USA was never part of the British Empire. Certain eastern states were individually British colonies, some of which (eg Virginia and Carolina) were actually named in honour of British sovereigns. Interestingly enough, these states have not been renamed in the 230+ years since independence.
The Duke and Duchess are actually visiting California I believe and that certainly was never part of the British Empire. I hope Lostlover doesn't hear about any visiting Spanish dignitaries. That would really finish him off.
John Adams, the lawyer and United States President who helped to frame the American Constitution, called the British Constitution
the most stupendous fabric of human invention in history.
Some parts of the British Constitution are unwritten. However many crucial parts of the Constitution are written down and have been for centuries. They are:
1) Common Law
2) The Coronation Oath
3) The Magna Carta 1215
4) Statute of Westminster 1275
5) The Petition of Right 1628, Declaration of Right and Bill of Rights 1689
6) The Act of Settlement of 1701
7) The Act of Union 1707
For the sake of brevity I will expound, just a little on two of the above:
1)
COMMON LAW
Established by Alfred the Great (AD 871- 899) Common Law has been developed by the British people for more than a thousand years. It is
common because it applies to everyone equally.
Common Law is grounded in the Ten Commandments and the Golden Rule - treat others as you would be treated. Common Law was developed by British people so they could settle their differences peacefully and fairly.
Common Law incorporates the Charter of Liberties (1100). The Charter makes the Sovereign subject to the law and affirms that no person is above the law. Common Law includes the Council of Westminster (1102), which ended slavery in England. Common Law protects the right established in the Petition of Right (1627) that no person can be arrested for disagreeing with the government. Common Law defends your property rights, your right to self-defence and your right to be secure in your own home -
your home is your castle.
Common Law establishes every person's right to a jury trial and the freedom of juries to declare a person innocent. If a jury believes that a person has been charged under an unjust law, it has the right to acquit. For this reason Common Law is superior to the statute law created by Parliament. In the 17th century the Lord Chief Justice ruled that juries have an inalienable right to freely decide guilt and innocence.
Common Law plainly states that judges are to be guided by precedent - the rulings of previous cases. They are not to make up the law. Where there is no precedent, Common Law dictates that decisions must be made according to principles of fairness recognized by Common Law.
Common Law contributes to the prosperity of Britain, the United States, Canada, Australia and New Zealand.
4.
The Statute of Westminster, AD 1275, would appear to be the foundational document that established Parliament. With the Sovereign and the Judiciary, Parliament forms the third branch of government. Its political parties, cabinet, prime minister and whips have gradually evolved as hoary traditions.