There was to be one further development in the constitutional monarchy which was to follow American independence. Until then, the King or Queen played an active role in the executive. The Ministers were not responsible to parliament; they were responsible to the King. So the model the Americans took was one where the head of state was also still head of government.
Paradoxically, it was the American War for independence which was to see the beginnings of what we recognize as the Westminster system, where the government is responsible to the House of Commons.
It was in March 1782 when, following the defeat of the army at Yorktown, the House of Commons voted that they "can no longer repose confidence in the present ministers." Lord North, who was Prime Minister, resigned. This was the beginning of the constitutional convention which became firmly established in the middle of the nineteenth century, that a government must retain the confidence of the House of Commons. This of course was the system which the British gave to their settled colonies in the mid nineteenth century.