He undertook, with Peter of Savoy, the Queen's uncle, the difficult task of extricating the King from the pledges which he had given to the Pope with reference to the Crown of Sicily; and Henry's writs of this date mention Montfort in friendly terms. But at the "Mad Parliament" of Oxford (1258) Montfort appeared with the Earl of Gloucester, at the head of the opposition. He was part of the Council of Fifteen who were to constitute the supreme board of control over the administration. The King's success in dividing the barons and in fostering a reaction, however, rendered such projects hopeless. In 1261, Henry revoked his assent to the Provisions of Oxford and Montfort, in despair, left the country. Simon de Montfort returned to England in 1263, at the invitation of the barons who were now convinced of the King's hostility to all reform, and raised a rebellion with the avowed object of restoring the form of government which the Provisions had ordained. Cancellation of debts (owed to Jews) was part of his call to arms. These "cancellations" involved massacres of Jews by his followers, to obtain their financial records, for instance in Worcester and London. The Worcester attack and killings were led by de Montfort's son Henry, and Robert Earl Ferrers. In London, one of his key followers John fitz John led the attack, and is said to have killed leading Jewish figures Isaac fil Aaron and Cok fil Abraham with his bare hands. He allegedly shared the loot with Montfort. 500 Jews died. His son Simon led a further attack on Jews in Winchester. Jews in Canterbury, were murdered or driven out in by a force led by Gilbert de Clare There was further violence in Lincoln, Cambridge, Wilton and Northampton. Each attack was aimed at seizure of the records of debts, stored in locked chests within each community, called 'archae'. Archae were legally mandated by the king for Jews to be allowed to conduct any business. They were destroyed or gathered for instance at Ely by the rebels. Henry quickly gave in and allowed Montfort to take control of the council. His son Edward, however, began using patronage and bribes to win over many of the barons. Their disruption of parliament in October led to a renewal of hostilities, which saw the royalists able to trap Simon in London. With few other options available, Montfort agreed to allow Louis IX of France to arbitrate their dispute. Simon was prevented from presenting his case to Louis directly on account of a broken leg, but little suspected that the King of France, known for his innate sense of justice, would completely annul the Provisions in his Mise of Amiens in January 1264.