Robert first attacked Worcester in February 1264, sacking the Jewish quarter, plundering the religious and private houses, and damaging the fences and lands of the Royal parks in the neighbourhood.

To Robert's extreme annoyance, Edward escaped, having made a truce with Henry de Montfort, Simon's son.

Prince Edward and the king having finally been captured gave Ferrers his opportunity, to gain the royal castles of Bolsover, Horston, and Tickhill, in Yorkshire.

Meanwhile, Edward continued under house arrest, and Montfort was working out an agreement for his release that included the surrender of large portions of his lands.

Montfort summoned Ferrers to the session of Parliament for January 1265, ordered him to surrender Peverel Castle, and accused him of "divers trespasses", after which he had him arrested and sent to the Tower of London.

In spite of Ferrers's activities against Prince Edward's estates, his support in the North Midlands was potentially useful to King Henry, as was his money.

Far from accepting his good fortune, in 1266 he joined a number of previous Montfortian supporters, including Baldwin de Wake, lord of Chesterfield, in a fresh rebellion.

Robert was, therefore, compelled to move northwards, crossing the River Amber, which was then flooded, reaching Chesterfield on 15 May 1266, just as d'Ayville arrived from Dronfield.

However, the Dictum of Kenilworth, issued in October 1266, provided that Ferrers could reclaim his lands in return for a redemption payment of seven times their annual value.

Although the chances of Robert finding such a sum were remote, Edmund and his associates made their position more secure by a move that was unlikely to have been intended by those who drafted the Dictum of Kenilworth.

There, in the presence of John Chishall, the chancellor, he was required to assign the lands to twelve manucapters[6] He was kept imprisoned at Richard of Cornwall's Wallingford Castle until the end of May and on 9 July the estate was transferred to Edmund.

In the time it would provide a considerable part of the revenues of the Duchy of Lancaster, while Ferrers was left virtually landless and deprived of his title.

Ferrers lived on for another ten years, during which he attempted to regain his estates, with little success, largely because the machinations at Cippenham had been quietly supported by the King and his council.

In 1274, when Edward, now King, returned to England, Ferrers pleaded that he had accepted the Kenilworth ruling, with its seven years' redemption period, but that Edmund had refused.

Ferrers argued that the 'agreement' was made under duress, but it was held that chancellor Chishall's presence at the signing gave it full legal validity.

Ferrers's case was dismissed and, although in 1275, he was able to recover his manor at Chartley (but not the castle), it marked the end of the great position of what had been one of England's most powerful families.

Sir Robert de Ferrers, sometime Earl of Derby, died shortly before 27 April 1279, and was buried at St Thomas's Priory at Stafford, in Staffordshire.

In Michaelmas term 1279 his widow, Eleanor, sued Edmund the king's brother for dower in a third of Tutbury, Scropton, Rolleston, Marchington, Calyngewode, Uttoxeter, Adgeresley, and Newborough, Staffordshire, and Duffield, Spondon, Chatesdene, and nine other vills named in Derbyshire, as well as other prominent landowners including Henry de Grenley (see Grindlay family);[7] Edmund appeared in court and stated he held nothing in Spondon or Chatesdene, and as regards the rest Eleanor had no claim to dower in them, because neither at the time Robert had married her nor any time afterwards had he been seised of them.