Ireland had been among the lands which Edward had received from Henry III in 1254. In the spring of 1256 la Zouche was sent there in service to Lord Edward, and soon afterwards he was appointed justiciar of Ireland under Edward, his first official mandate being dated 27 June 1256. In 1257 he was still in Ireland. On 28 June 1258 he received a mandate from the king, now under the control of the barons, not to admit any justice or other officer appointed by Edward to Ireland unless the appointment had the consent of the king and the barons. However, he ceased to hold office soon after this, Stephen Longespee being found acting as justiciar in October 1258. During the barons' wars la Zouche adhered to the king. He was on 9 July 1261 appointed High Sheriff of Northamptonshire, receiving in October a letter from the king urging him to keep his office despite any baronial interlopers. He remained sheriff until 1264, and sometimes ignored the provisions of Magna Carta by acting as justice itinerant in his own shire and also in Buckinghamshire and Hampshire. In 1261 he was also made justice of the forests south of Trent, and in 1263 king's seneschal. In April 1262 he held forest pleas at Worcester. On 12 December 1263 he was one of the royalist barons who agreed to submit all points of dispute to the arbitration of Louis IX. According to some accounts he was taken prisoner early in the battle of Lewes by John Giffard. He escaped almost immediately and took refuge in Lewes Priory, where he is said to have been found after the fight disguised as a monk. In the summer of 1266 he was one of the committee of twelve arbitrators appointed to arrange the terms of the surrender of Kenilworth Castle. On 23 June 1267, after the peace between Henry III and Gilbert de Clare, 8th Earl of Gloucester, he was appointed warden of London and constable of the Tower. He continued in office until Michaelmas, whereupon his tenure was prolonged until Easter 1268. In 1270 la Zouche had a suit against Earl Warenne with regard to a certain estate. On 19 June the trial was proceeding before the justices at Westminster Hall, and la Zouche seemed likely to win the case. He was murderously attacked by Earl Warenne and his followers. Roger, his son, was wounded and driven from the hall; Alan himself was seriously injured and left on the spot.