The king and his son at once crossed the channel to Amiens, where the French king was to hear both sides.  A fall from his horse prevented Leicester attending the arbitration, and the barons were represented by Peter Montfort, lord of Beaudesert castle in Warwickshire, and representative of an ancient Anglo-Norman house that was not akin to the family of Earl Simon.  Louis did not waste time, and on January 23, 1264, issued his decision in a document called the “Mise of Amiens,” which pronounced the Provisions invalid, largely on the ground of the papal sentence.  Henry was declared free to select his own wardens of castles and ministers, and Louis expressly annulled “the statute that the realm of England should henceforth be governed by native-born Englishmen”.  “We ordain,” he added, “that the king shall have full power and free jurisdiction over his realm as in the days before the Provisions.”  The only consolation to the barons was that Louis declared that he did not intend to derogate from the ancient liberties of the realm, as established by charter or custom, and that he urged a general amnesty on both parties.  In all essential points Louis decided in favour of Henry.  Though the justest of kings, he was after all a king, and the limitation of the royal authority by a baronial committee seemed to him to be against the fundamental idea of monarchy.  The pious son of the Church was biassed by the authority of two successive popes, and he was not unmoved by the indignation of his wife, the sister of Queen Eleanor.  A few weeks later Urban IV. confirmed the award.

The Mise of Amiens was too one-sided to be accepted.  The decision to refer matters to St. Louis had been made hastily, and many enemies of the king had taken no part in it.  They, at least, were free to repudiate the judgment and they included the Londoners, the Cinque Ports, and nearly the whole of the lesser folk of England.  The Londoners set the example of rebellion.  They elected a constable and a marshal, and joining forces with Hugh Despenser, the baronial justiciar, who still held the Tower, marched out to Isleworth, where they burnt the manor of the King of the Romans.  “And this,” wrote the London Chronicler, “was the beginning of trouble and the origin of the deadly war by which so many thousand men perished.”  The Londoners did not act alone.  Leicester refused to be bound by the award, though definitely pledged to obey it.  It was, he maintained, as much perjury to abandon the Provisions as to be false to the promise to accept the Mise of Amiens.  After a last attempt at negotiation at a parliament at Oxford, he withdrew with his followers and prepared for resistance.  “Though all men quit me,” he cried, “I will remain with my four sons and fight for the good cause which I have sworn to defend—­the honour of Holy Church and the good of the realm.”  This was no mere boast.  The more his associates fell away, the more the Montfort family took the lead.  While Leicester organised resistance in the south, he sent his elder sons, Simon and Henry, to head the revolt in the midlands and the west.