The last post described English society as a graduated hierarchy ranging from landless laborers at the bottom rising to the monarch at the top. The most fundamental division in the layers of this hierarchy separated the nobles from the commoners. This division was mirrored in the constitutional arrangement of England.
The contemporary understanding of the word constitution, especially in the United States, suggests a written document described the structure and powers of government. Often it is used merely to describe the composition or structure of something, regardless of whether or not that composition is described in any document. Such is the case with England's constitution. England has no written constitution.
It's constitution, or structure of government grew from historical developments going back to to the eleventh century. English kings occasionally assembled a great council of advisers consisting of bishops, earls, and barons. In the thirteenth century, kings began inviting those he deemed the "knights of the shires" to meet with the great council and the monarch to discuss financial matters. In 1341, the nobility began meeting separately from the knights. The former eventually evolved into the House of Lords, Temporal and Spiritual. The latter evolved into the House of Commons.
As is often the case, the "theory" of government followed and justified the historical development of the government. The English saw their government as mirroring or better yet embodying the people. The House of Lords represented the nobility; the House of Commons represented the English people as as whole.
The English also conceived of their constitution as a "mixed regime" that included the three fundamental types of constitutions. Aristotle classified constitutions into three fundamental types: monarchy, aristocracy, and democracy. English political theorists saw all three of these forms in the English constitution. The king represented monarchy, the House of Lords represented aristocracy, and the House of Commons represented democracy.
When the English colonist set up their provincial governments, they patterned them loosely on the English Parliament. In fact, colonial assembles were often spoken of as "little Parliaments." After independence, the Americans established state governments and a national government under the Constitution of 1787 that preserved the structure of English government but assumed a whole new meaning under American social conditions.