All of this theory is based on fundamental misconceptions. (No pun intended with 'fundament', honest.) Firstly, according to his biographer Professor David C. Fowler, John Trevisa was born in about 1342, fifteen years after Edward II's alleged murder. Secondly, he didn't come from the village of Berkeley but from Cornwall, probably Trevessa in the parish of St Enoder between Newquay and St Austell, hence his name. Thirdly and most importantly, the Thomas, Lord Berkeley he served as chaplain was not Edward II's custodian of 1327, but his grandson of the same name.
Thomas Berkeley, the custodian of 1327, died in October 1361, when Trevisa was about nineteen. According to Professor Fowler, the earliest documented evidence of a connection between Trevisa and the lords of Berkeley is Trevisa's dedication in his translation of the Polychronicon, which he completed on 18 April 1387, to Thomas, Lord Berkeley the grandson. Trevisa was still at Oxford when he finished his translation, and the first certain evidence that he was living at Berkeley comes in 1388 - in other words, twenty-seven years after the death of Edward II's custodian Lord Berkeley, and a whopping sixty-one years after Edward's supposed murder.
Thomas Berkeley the grandson was born on 5 January 1353, was eight years old when his grandfather of the same name died in 1361, succeeded as Lord Berkeley when he was twenty-one in January 1374, and lived until July 1417. His ancestry is fascinating: grandson of Edward II's custodian, grandson also of Hugh Despenser the Younger, great-grandson of Roger Mortimer. Thomas was the eldest son of Maurice Berkeley, himself the eldest son of Thomas Berkeley the Elder and born sometime in 1330, about two and a half or three years after Edward II's alleged murder in his father's castle. Maurice married Hugh Despenser the Younger's daughter Elizabeth in August 1338 when he was eight, and died in June 1368, supposedly of old wounds received at the battle of Poitiers in 1356. Whether the Thomas Berkeley of 1327 ever told his son Maurice anything about Edward II's fate, and whether Maurice passed this information on to his own son - or to his wife Elizabeth Despenser, Edward's great-niece - is a matter for conjecture. Given that John Trevisa copied the story of the red-hot poker, which is an utterly ludicrous fabrication, if his patron Lord Berkeley did know the truth of what happened to Edward II, evidently he didn't tell Trevisa.
If people would just think a little before repeating the myth 'Trevisa was Lord Berkeley's chaplain and must have heard the truth about Edward's murder' they'd realise that as Trevisa translated the Polychronicon into English, the Lord Berkeley of the dedication cannot be Thomas Berkeley the grandfather. He lived in an England where the French language still dominated among the nobility, and the odds that he would have wanted to read a text translated into English are remote. For his grandson, however, who grew up in a world where English was becoming more and more significant as a literary and courtly language, it does make sense. If people would just think a little, they'd realise that a man with the last name 'Trevisa' is not likely to have come from Berkeley. If people would just do a little basic research - I found Trevisa's correct date of birth in about five seconds on Google Books - they'd discover that he was not alive in 1327, did not serve as confessor to Lord Berkeley the grandfather and arrived at Berkeley Castle six decades after Edward II's supposed murder. But then, why bother to do such basic research when it's so easy to mindlessly repeat the unfounded assumptions of earlier writers? And it always amuses me when I see writers solemnly declare that Trevisa was a child in Berkeley village when Edward was imprisoned at the castle there, as though this means that Trevisa therefore had inside knowledge of the king's fate. Are we supposed to think that Lord Berkeley was in the habit of sharing state secrets with local village boys?
By the time John Trevisa arrived at Berkeley in the late 1380s, there couldn't have been anyone alive there who knew the truth about Edward II's fate, and he had no more insight into the affair than anyone else. As for Ranulph Higden of the Polychronicon, he was a monk of Chester and knew no more about Edward's death than anyone else did either, and just because both men repeated the red-hot poker story is not proof that it's true.