In October, Edmund was once more employed in a move against Badlesmere, when he took part in a siege on Leeds Castle in Kent, which was held by Badlesmere. After Badlesmere was forced to surrender, hostilities moved to the Welsh Marches, where Roger Mortimer and others were in open revolt. Once confronted with the royal army, Mortimer surrendered without a fight, and attention turned to the leader of the baronial opposition, Thomas of Lancaster. Edmund, who had taken part in the Marcher campaign, was now ordered, with the Earl of Surrey, to take Lancaster's castle of Pontefract. On 17 March 1322, Lancaster was captured after his defeat at the Battle of Boroughbridge, and brought to Pontefract. Here, Edmund was on the jury that condemned him to death for treason.