Peter was again in England in 1261, when he was one of three persons elected on the king's part to compromise some disputes with the barons (Ann. Osen. p. 129). His past history necessarily made him a royalist partisan during the barons' wars, and his border diocese, where the marchers and Llywelyn of Wales took opposite sides, was exposed to the fiercest outbursts of the strife. Late in 1262 Llywelyn threatened Hereford, and Peter, on the pretext of a fit of the gout, kept himself away from danger at Gloucester, while providing the castle of Hereford with garrison and provisions. In June 1263 Henry visited Hereford and wrote angrily to the bishop, complaining that he found in that city neither bishop, dean, official, nor prebendaries; and the letter peremptorily ordered him to take up his residence in his cathedral city under pain of forfeiture of temporalities (Wilkins, Concilia, i. 761). Peter was forced to comply; but the result justified his worst fears. When regular hostilities had broken out in May 1263 between Montfort and the king, he was the very first to bear the brunt of the storm. The barons swooped down on Hereford, seized him in his own cathedral, robbed him of his treasure, slew his followers, and kept him a close prisoner at Eardisley Castle (Liber de Antiquis legibus, p. 53; Rishanger, p. 17, Rolls Ser.; Cotton, p. 139). The Savoyard canons whom Peter had introduced into the cathedral shared his fate (Flores Hist. ii. 480). Even the royalist chronicler Wykes (p. 134), though rebuking the barons for sacrilegiously assaulting God's anointed, admits that Peter had made himself odious to the realm by his intolerable exactions. The marcher lord, John Fitzalan of Clun, now seized Peter's castles at Bishop's Castle and Ledbury North, and, being on the king's side, was enabled to hold them until the bishop's death, six years afterwards (Swinfield Roll, p. xxii). Moreover, Hamo L'Estrange, castellan of Montgomery, took violent possession of three townships belonging to Ledbury North, and alienated them so completely from the see that in the next reign they still belonged to Llywelyn of Wales. As both these marches were on the king's side, it looks as if Peter was made a scapegoat of the royalist party. It is probably during his present distress that Peter alienated all claims to certain churches which he had hitherto contested with St. Peter's Abbey, Gloucester (Hist. et Cart. Mon. Glouc. ii. 276, 284, Rolls Ser.)
On 8 Sept. the king and the barons patched up an agreement, and Peter, with his companions in misfortune, was released (Flores Hist. ii. 484; Rishanger, De Bello, p. 14). Before the year was out he accompanied Henry III to await the arbitration of St. Louis at Amiens (Flores Hist. ii. 486; Rishanger, De Bello, p. 17; Ann. Tewkesbury, pp. 176, 179). After the mise of Amiens he still lingered on the continent, being disgusted with his unruly diocese, whose temporalities were still largely withdrawn from his control. In February 1264 he obtained from the pope an indulgence that, in consideration of his imprisonment and the other ills he had suffered ‘at the hands of certain sons of malediction,’ he should not be cited before any ordinary judge or papal legate without special mandate (Bliss, i. 410). After the battle of Lewes he was with Queen Eleanor and the exiles at Saint-Omer, hoping to effect an invasion of England (‘Ann. Lond.’ in Stubbs's Chron. of Edward I and Edward II, i. 64, Rolls Ser.)
Before the final triumph of the royalist cause, Peter retired to Savoy, and never left again his native valleys. He had always kept up a close connection with his old home. Besides his ancestral estates he had acquired some ecclesiastical preferment in Savoy. Up to 1254 he held the Cluniac priory of Ynimont in the diocese of Belley, which in May 1255 he exchanged for the priory of Sainte-Hélène des Millères (Bliss, i. 301). On 7 Sept. 1255 Boniface granted to the new prior the castle of Sainte-Hélène, to be held of him as a fief.
It was now that Peter published the statutes for his college of canons near Aiguebelle, and completed the construction of the buildings destined to receive it. He dedicated his foundation to St. Catherine, and established in it a provost, precentor, treasurer, and ten other canons, five of whom were necessarily priests, and who were to perform the service according to the use of Hereford. The statutes, dated 21 April 1267, were published for the first time by M. Mugnier (pp. 299–307), who points out (p. 233) that Peter pointedly abstained from obtaining the sanction or recognition of his acts from the bishop of Maurienne, the diocesan. Soon afterwards he drew up his will. To his nephew, Peter of Aigueblanche—who had succeeded to the lordship of Briançon and the headship of the house, and was at a later period the favourite friend of Peter of Savoy—he left nearly all the property that was not bequeathed to the college of St. Catherine. The witnesses to the will included several canons of St. Catherine's. He died on 27 Nov. 1268, and was buried, as he had directed, in his collegiate church, where, in the fifteenth century, a sumptuous monument of bronze
