The coronation oath, which Edward took in French—a Latin version was available, but since the entire court spoke French, it made sense to forsake the Latin—contained a fourth clause whose ambiguity led to much discussion. This clause had been added by the barons to create a special obligation for Edward. (This clause remains in the oath even now.) It states that the king would "uphold and defend the laws and the righteous customs which the community of your realm should determine."
The debate began over the composition of the "community." The barons insisted they were the community, and that they would determine the "laws and righteous customs." That was the obligation that they invoked when objecting to Edward's favor of Gaveston. They pressured Edward until, on 18 May 1308, he avoided civil war by signing letters patent that stripped Gaveston of his titles and exiled him from England by 25 June. Archbishop Winchelsey weighed in, promising to excommunicate Gaveston if he failed to quit England.
Edward didn't leave his friend high and dry: he appointed him Lord Lieutenant of Ireland, gave him blank royal charters, and gave him a royal send-off from Bristol. Gaveston was no fool: he proved to be a competent and generous lieutenant, and suppressed a couple rebellions. His time in England was not over, either: when the barons presented Edward with a list of demands at the Parliament of 27 April 1309, Edward promised to grant them their desires...if he were allowed to bring back Gaveston.
Gaveston was in no way chastised by his exile, and his return brought with it a return of the behavior objectionable to the peerage. A further set of demands made of Edward, the Ordinances of 1311, included Gaveston's exile again, under penalty of outlawry if he should return. But return he did in late 1311, setting off his excommunication.
The nobles of England were all too happy to put their resources into finding and capturing him. Some of his enemies acted honorably, some not. The story includes a king and a criminal "going on the run," and I'll share it with you next time.