The abbey had a long standing dispute with the Archbishops of Canterbury.
'Ultra portam' meant a gatehouse tower - over the gate rather than 'without' as translated in the Calendar.
The abbots were not summoned to parliament because they were mitred, but because they held their lands in capite per baroniam, and received their temporalities from the king; and of these, only such had this privilege as were especially, as through the king's favour, called thither by writ. (Hasted p. 158-77n29)
Perhaps the most curious incident in the history of the abbey is the story of Peter de Dene. He had been a distinguished ecclesiastical lawyer, and was at one time counsel to the abbey, to which he was a generous benefactor; but, getting into trouble in politics, in 1322 he sought admission there as a monk, and was received under a relaxed form of profession with many privileges, after bringing a present of silver and making his will in favour of the abbey. Eight years later he wished to leave it again, but the abbot refused to permit him; and he thereupon fled to Bishopsbourne, but a few days later was captured and brought back. He managed, however, to appeal to the pope, who in 1331 ordered the prior of the cathedral to inquire into the matter. Great resistance was offered to the prior, and it was not till he had entered the abbey church with a powerful force that he was able to get any conversation with Peter at all; and then from a distance, surrounded by monks, Peter declared himself perfectly contented. It seems certain that Peter must have been forcibly detained and impersonated by someone else, but nothing more could be done for him; and the abbot and monks received pardon from the king for what they had done. (VCH)