There are 3 ways MPs could vote down Article 50 - and Theresa May has only ruled out one of them
That last part is crucial: There is a pro-Remain majority inside the House of Commons, and if parliament were to ever get a substantive vote on Article 50 it could stop Britain leaving the EU. In fact, the referendum is merely advisory to government and the House of Commons is well within its constitutional rights to ignore it.
So May ruling out a parliament vote on Article 50 is a crucial stake in the ground for her.But the former director-general of the Council of the European Union's Legal Service says the House of Commons may yet get a vote on Article 50. In a column for the Financial Times, Jean-Claude Piris notes that there are two potential opportunities for MPs to scotch Article 50. The vote that May ruled out - on whether parliament should trigger the Article 50 request to leave - is merely the first one, the one everyone already knows about.
The second, less well-known opportunity is when the UK has negotiated its exit package and needs to ratify the deal after Article 50 is triggered but before the UK is booted out, Piris says (emphasis ours):
Triggering Article 50 allows talks to begin in order to negotiate and conclude a "withdrawal agreement" with the EU (only on the terms of the divorce; not on post-Brexit relations). As a treaty, its entry into force would require ratification by the House of Commons. That entry into force would entail Brexit.
Failure to ratify the deal could force the government to use the loophole that lets Britain reverse its request after it has triggered Article 50. Article 50 triggers aren't final - a country can change its mind any time during the two-year period before the exit clock runs out.
And then, of course, there is the UK Supreme Court case which may require a vote in parliament as a matter of law.
So that is three potential ways that MPs could get an Article 50 vote - and May has only ruled out one of them.In other words, for the Remain camp, the battle isn't over yet.