I don't know about all the Arthurian stories, but it was supposedly Joseph of Aramathea, not Jesus, that took the 'holy grail' to England. The 'graal' was an earlier story by Chretien des Troyues, but first became 'holy grail' and connected to Joseph of Ar. in a peom by a Frenchman Robert de Boron about 1190 A.D. Camelot doesn't turn up until later French stories. A recent book come to the tentative conclusion that Camelot might have been Viriconium in Wales, abandoned about 520 A.D., probably right after the civil war that culminated at the battle of Camlann, where Arthur and Modred/ Mordred/ Mawdred were killed. [This assumes that there was an Arthur and Modred.]