The inspeximus and its witness list provide important evidence about the parliament called by Simon de Montfort, earl of Leicester, which took place at Westminster, between the octaves of Hilary (20 January) and c.14 March 1265.5 The parliament was held during the concluding stage of the period of reform and rebellion. The previous year, on 14 May, Montfort had defeated and captured Henry III and his son, the lord Edward, at the battle of Lewes.6 He and his confederates had subsequently seized the reins of government and established a council of magnates, bishops and knights to rule in the king’s name. The new regime, though, rested on unsteady foundations. The seizure of royal power by subjects was radical and hard to justify. When a council was first imposed on Henry by a court coup, in 1258, and briefly re-imposed, in 1263, the reformers had claimed that the king had given his consent. Montfort’s victory at Lewes meant that this line was now insupportable.7 The new regime was founded on a precarious military superiority and lacked the consent not only of the king but also much of the comital and baronial elite. Meanwhile, the lord Edward’s allies among the barons of the Welsh marches threatened a counter-attack. The future of Montfort’s government rested on the earl’s ability to mobilise a broader base of support, amongst the senior churchmen who could lend his regime moral authority as well as the county knights and townsmen who could implement its rule on the ground and defend it from a royalist resurgence.8 To this end Montfort had summoned to parliament 120 prelates as well as two knights elected from every county and citizens from the towns and Cinque Ports.9
Sophie Ambler, ‘Feature of the month: March 2014 – Henry III’s Confirmation of Magna Carta in March 1265’, The Magna Carta Project [http://magnacartaresearch.org/read/feature_of_the_month/Mar_2014 accessed 04 March 2014]