What disagreement began the struggle between Thomas Becket and Henry II in 1163?

The struggle between Thomas Becket and Henry II began in 1163, shortly after the king’s return to England from Normandy. While tensions grew over a tax proposal and Becket’s excommunication of a leading baron, the primary conflict centered on the issue of "criminous clerks"—members of the clergy accused of committing crimes.1

Historically, accused clerics enjoyed the privilege of standing trial before a bishop in an ecclesiastical court, where they typically received more lenient sentences than in secular courts. Henry II sought to curb this power, contending that clerical crime was rampant and required the oversight of royal courts for punishment. Becket, however, took a rigid stance based on canon law, arguing that a clerk should not be punished twice for the same fault—once by the church and again by secular authority. This disagreement escalated into the formal crisis of the Constitutions of Clarendon in 1164, which sought to codify royal control over the church.123