1285 he was sent on a mission to Scotland (Cal. Pat. Rolls, 1281–92, p. 192). Between September and November 1289 he was engaged in negotiating the treaty of Salisbury with the Scots (ib. p. 328; Cal. Doc. Scotl. i. 107). On 14 Feb. 1290 he received protection on going to Scotland as the king's envoy (ib. p. 343), and on 20 June was appointed with Antony Bek [q. v.], bishop of Durham, to treat with the guardians of that country (ib. p. 372; Cal. Doc. Scotl. i. 158). On 18 July they concluded the treaty of Brigham (ib. i. 162). On 28 Aug. he was nominated proctor for the king's son Edward on the occasion of his expected marriage with the little queen of Scots, and next day was one of an embassy appointed to treat with her father, Eric of Norway (ib. p. 386). During his absence he was respited from paying his debts (ib. i. 180). He strongly upheld the candidature of John Baliol, his son-in-law, for the Scottish throne.
On 16 Sept. 1295 Warenne was appointed custodian of the sea coast (Cal. Pat. Rolls, 1292–1301, p. 147). On 5 Oct. he was made, jointly with Anthony Bek, custodian of the counties beyond the Trent (ib. p. 152), and next day of Bamburgh Castle (ib. p. 151). On 18 Oct. he nominated attorneys until Easter, as being about to go to Scotland on the king's service (ib. p. 156). He was therefore on the borders already when, in the spring of 1296, Edward began his great invasion. A month after the capture of Berwick, on 30 March, Edward sent Warenne and William Beauchamp, earl of Warwick, to attack the castle of Dunbar. Arriving outside the walls on 23 April, on the 27th they defeated the Scots army that sought to relieve the town (Hemingburgh, ii. 103–4), and next day forced Dunbar to surrender. Warenne accompanied Edward in his march through Scotland. He was at Montrose on 10 July, and went back with Edward to Berwick. There on 22 Aug. Warenne was appointed ‘warden of the kingdom and land of Scotland.’ On 23 Nov. 1296 he was at Jedburgh (Hist. Doc. Scotl. ii. 245, misdated 1297 by the editor), but early in the winter Warenne quitted his government on the plea that the climate made it impossible for him to remain without danger to his health (Hemingburgh, ii. 127). He made a merit of remaining in the north of England. It was during his absence that Sir William Wallace [q. v.] rose against the English in May 1297. Even then Warenne delayed his return on various excuses. ‘And know, sire,’ he wrote, ‘that the delay which we have made will cause you no harm whatever, if God pleases’ (Hist. Doc. Scotl. ii. 183–4; cf., however, Hemingburgh, ii. 127, ‘quod fuit nobis in posterum fons et origo mali’). On 14 June the king ordered Warenne to his post (Hist. Doc. Scotl. ii. 184–5); it was not until the end of July that he reached Berwick (ib. ii. 204, 223). Even then he lost time by sending his grandson, Henry Percy, to negotiate with the Scots. On 14 Aug. the king, losing patience, made Brian Fitzalan [q. v.], lord of Bedale, governor of Scotland (Fœdera, i. 874). Edward then went to Flanders. Fitzalan, however, showed such unwillingness to take office that on 7 Sept. the regents begged Warenne to continue in his command (Hist. Doc. Scotl. ii. 230). During these transactions Warenne crossed the border. His want of men and money probably extenuates, though it does not excuse, his remissness. Late in August he advanced to Stirling. He was still unwilling to fight, and gladly negotiated with the steward of Scotland, who counselled delay and offered to bring back the insurgents to the king's peace. Ultimately Warenne found that the steward could not or would not redeem his promise. Meanwhile the Scottish army under Wallace had taken up a position north of the Forth on the hills overlooking the narrow bridge of Stirling. On 11 Sept. the clamour of his soldiers forced Warenne to fight (Hemingburgh, ii. 135). Though warned of the certain consequences, he foolishly sent his men over the bridge to attack the enemy on the other side. When the van had crossed over, Wallace fell upon it and cut it off almost to a man. The demoralised English army melted away. The steward of Scotland joined Wallace. Warenne threw a garrison into Stirling and escaped with a few followers to Berwick (Lanercost, p. 190). Thence he hurried to England, begging for help from the regency. On 27 Sept. he was at York (Hist. Doc. Scotl. ii. 232–3). The Scots then occupied Berwick, only the castle holding out. Later in the year Warenne joined with other royalist earls in protecting his nephew Norfolk and the Earl of Hereford against the wrath of Edward I (Hemingburgh, ii. 154).
Despite his past blunders, on 10 Dec. Warenne was again appointed captain of an expedition against the Scots (Hist. Doc. Scotl. ii. 249–50). This time he showed greater haste, taking out on 12 Dec. letters of attorney until Easter (Gough, Scotland in 1298, p. 53), and receiving on 14 Dec. letters of protection as about to go to Scotland (ib. p. 16). His debts and pleas were respited until his return. On 14 Jan. he held a council at York, where the charters which the regents
