As colonial agent for multiple colonies, Benjamin Franklin was a loyal and devoted British subject, though he had long supported colonial rights within the empire. He had worked as a mediator, in fact, between the colonies and the metropole throughout the imperial crisis that began after the French and Indian War.
A series of events rapidly changed Franklin's views, however, all of which happened rapidly in late 1773 and early 1774. First, news of the Boston Tea Party reached England, an event that led Parliament to pass a series of harsh measures intended to punished the recalcitrant colonists in Boston. These Intolerable Acts were bad enough, but Franklin also suffered a major embarrassment when it was revealed that he had leaked the contents of several letters by Massachusetts governor Thomas Hutchinson. These events turned many of Franklin's friends in Parliament and on the Privy Council against him, and in January 1774, he endured the last straw, a public castigation in front of the Council and many other members of George's III's court in the so-called "cockpit." Franklin stood silent before the council as member after member, especially Solicitor General Alexander Winterburn, subjected him to withering abuse.
As historian Gordon S. Wood observes, this was a turning point for Franklin and for the relationship between the colonies and Britain in general. The Coercive Acts passed in the wake of the Boston Tea Party angered and unified the colonies in a way hitherto inconceivable. And alienating Franklin made things worse:
By publicly humiliating Franklin...the British government...virtually destroyed the affections of the only colonist in England who might have brought about reconciliation.
Source: Gordon S. Wood, The Americanization of Benjamin Franklin (New York: Penguin Books, 2004) 146-147.