So, Judaism was the founding major faith at Roman Londinium. It was also the major faith prior to the Roman presence where old Gaelic French was the predominant language. The story, rumors about or the message of the Messiah would have existed at the time of the Roman occupation in 43 A.D. but the major monotheistic religion was clearly Judaic.  Christianity is Judaic in essence but would not become a faith in its own right until much later on.