Magna Carta regulated the operation of royal government. Later in the reign of Henry III, calls began to be made for more radical reform. Henry III was criticised for being too generous to his close friends and family, handing out important jobs to them and protecting them from the law, at the expense of everyone else.
During Henry III’s reign, Parliament became increasingly important. Parliament was the name given to the occasions when all the barons met with the king and each other, usually at Westminster, but also elsewhere. The idea grew up after Magna Carta that the king could only gain extra taxes by asking the barons first. As the king needed money, he called the barons to parliament much more frequently than ever before. In return for giving taxes, the barons asked for reforms in government in return. In particular, they wanted to be able to choose the king’s ministers for him, and they wanted him to follow their advice, which he did not do.
A scheme of reform was eventually implemented in 1258 as a result of a range of factors including: tensions between factions at the royal court, widespread famine, military failure in Wales, and enormous debts the king had accrued with the Pope by agreeing privately and without consent of parliament, to pay for an army to conquer Sicily. This was added to already-strained royal finances. A group of leading barons, including Richard de Clare, earl of Gloucester, Roger Bigod, earl of Norfolk and Simon de Montfort, earl of Leicester, and others, acted jointly to force reform on the king.