Hereford, Gloucester, and Bristol, returning south to assault Windsor Castle. They were joined by Simon de Montfort, beginning the Second Barons' War. They marched into Kent, attacking the Cinque Ports. By August 1263 the Marcher Lords were in negotiations with Edward, having been unnerved by de Montford's plan to ally with the Welsh, and they swore an oath to the king on the 18th. From this point onwards Leybourne was a loyal servant of the king, and swiftly returned to royal favour. In September he was made Steward of the King's Household, Keeper of Kent, Surrey and Sussex, and in December was appointed Lord Warden of the Cinque Ports and made High Sheriff of Kent. In October 1263 he was one of those who sealed the agreement between Henry and Louis IX, and travelled with the king to France at the end of the year. During the second half of the conflict with de Montfort, Leybourne fought at the Battle of Northampton and as a defender at the siege of Rochester Castle, where he was badly wounded. He fought at the Battle of Lewes with the other marcher lords, who were allowed to go free after their defeat on the condition that they return to stand trial at the next Parliament. When they failed to do so, de Montfort sent a military expedition which failed to defeat them. So they remained a thorn in the side of de Montfort throughout the rest of the war. In December 1264 he was given a safe conduct to visit the king, and then in May 1265 he spoke with Edward, helping organise his escape from Kenilworth Castle on 28 May. Leybourne subsequently fought at the Battle of Evesham, reportedly saving the king's life, and for the two years of conflict after Evesham served as Edward's principal lieutenant. In August 1265 he was made keeper of Westmorland, in October he was given custody of Carlisle Castle, made High Sheriff of Cumberland and trusted with subduing London on behalf of the king. In November he fought the rebels in Kent, and in January 1266 he recaptured Sandwich, serving as Edward's deputy for the capture of the other Cinque Ports. Along with Edward he besieged and captured Winchelsea, fighting off rebels across the Thames in May. He was knighted in September, with the king ordering that he should be received everywhere 'with due honour as the