There is simple omission from your list: May's government has a working majority of 16. Without a sizeable number of defectors, Article 50 is a fait accompli; it isn't contingent on what the opposition do. Don't ask the Tories to put the country (that's the UK not just England), logic or reason before the interests of the party. They have neither the moral courage nor the inclination. A free vote for Labour MPs is pointless unless all other parties do the same; on its own it would be futile. In essence, short of a serious Tory rebellion or a dramatic economic collapse (highly unlikely before March - that'll come later), there is nothing that the opposition parties can do to divert May from her preferred course. If WTO is the chosen option, they'll rubber stamp it.

The symbols that bound the inscription are cross potents. This same symbol was used by the Knights (Order) of the Holy Sepulchre - 1099 - Present. If that's the case, particularly given that sword is contemporaneous with the Crusades, then the inscription is likely to be religious as suggested by BlackthornIX.