Historians do not think like lawyers. Colonial Whigs frequently did. The constitutional theory of the American Revolution has never been given the credit it deserves. This is the thesis in John Phillip Reid, In defiance of the law (Chapel Hill, 1981). and I have borrowed heavily from his text in this page. This page comments on the constitutional arguments of the revolutionists. 

It is not known generally today by academic historians that in 1770, the English "Constitution" did not mean what it does today. Today the English Constitution is known as whatever Parliament says it is. Not so in 1750, according to many lawyers on both sides of the Atlantic. Valid legal arguments were made that the English Constitution was a unwritten system of customary restraints on what the King and the governing body could do.

Consider Lord Camden. In 1766, he was Chief Justice of one of the central common law courts and about to become Lord Chancellor.. At that time he warned Parliament that there were steps, including taxing the American Colonies, that it could not take legally. Camden agreed with the theory of the Massachusetts lawyers: that the English Constitution was a system of customary restraints on what the King and the governing body could do. And that customary restraint made it legally improper to tax without the consent of the representatives of the English persons to be taxed. Lord Camden, "House of Lords Debate of 10 Feb 1766," in Parliamentary History (1766), 168.

It is necessary for us to understand that the constitutional case of 18th Century American lawyers and Whigs was based on the same unwritten constitution that 17th Century English lawyers and Whigs had used to attack Charles I and James II. In fact an English writer could say in 1768, "The late unhappy Stamp Act made here, to operate in America, was certainly as unconstitutional a measure as King James II's dispensing power."  "Stamp Act is unconstitutional," in Gentlemen's Magazine (1768), 356.

For example, Oliver Saint-John, Solicitor General of England, in 1641, before the English Civil War commenced, told the Lords that the law could not proceed in subversion of the unwritten constitution. Oliver Saint-John, "Argument of Law," (1641), 20.

After the glorious Revolution of England John Toland wrote, in 1701 "Parliament neither has nor ought to have an arbitrary power over the lives, liberties, or fortunes of the subjects, and should they manifestly appear to aim at such an execrable design, the whole people may justly call them to account." Toland, Anglia Libera. 4.

When the British put a standing British army in the colonies, and defended the constitutionality of their standing army in America on the grounds that it was sanctioned by Parliament — American lawyers thought in terms of 17th Century English theory. The American colonists, in the 1700's, found their constitutional arguments in the arguments of Sir Edward Coke, John Hampden, and John Pym.  Americans, and also some English, took the position that a standing army was unconstitutional in the colonies. The Americans argued that Parliament alone could not give a standing army constitutional sanction. 18th Century Americans 

The Imperial Army in America was a constitutional violation, according to the American lawyers. American lawyers were appealing not to a political theory of what should be; they appealed to what they regarded as a British customary constitution that ordained the legally permissible. Consider a speech of Lord Chancellor Hardwick, to the House of Lords in 1756 3 in which he stated "A standing army in time of peace, execution of Martial Law in a time of peace, are against law." Lord Chancellor Hardwick was not only the Lord Chancellor at the time he spoke but he had been Chief Justice of the King's Bench, privy counselor, Solicitor General of England and a Bencher of Lincoln's Inn. He was there for one of the most prominent common law lawyers of the Century. In short, to the extent that Chancellor York was speaking generally, Chancellor York agreed with the Massachusetts lawyers' argument that the use of British troops as a standing army available "at home"  to the home government  was an unconstitutional use of force. Lord Chancellor Hardwick, "Lords Debates of 24 May 1756," in Parliamentary History (1756).  [But England in 1756 was starting to distinguish between the home island of England and the "conquered lands" which they said did not have the rights of the home island.]

References

Camden, Lord. "House of Lords Debate of 10 Feb 1766." In Parliamentary History, 168: House of Lords, 1766. 

Hardwick, Lord Chancelor. "Lords Debates of 24 May 1756." In Parliamentary History, 727 - 28 and 742 - 43, 1756. 

Reid, John Phillip. In defiance of the law. Chapel Hill: Univ. of North Carolina Press, 1981. 

Saint-John, Oliver. "Argument of Law." 1641. 

"Stamp Act is unconstitutional." In Gentlemen's Magazine, 356, 1768. 

Toland. Anglia Libera.