In March, Britain's departure from the European Union began with the triggering of Article 50. But can it be stopped?
The question is a particularly valid one, given the possibility of Britain emerging from the two-year negotiation period without securing a good deal from Brussels. In light of negative reports about Theresa May's meeting with Jean-Claude Juncker last week, Remainers will argue it's a more relevant question than ever.
Many of those opposing Brexit will argue that revoking Article 50, and thus cancelling Brexit itself, is preferable to ending up with a deal that's against Britain's interests. In fact they'd probably argue it's the best option for Britain, no matter what deal we end up with.
Yet there's no precedent for reversing Article 50. The clause was only introduced in 2009, under the terms of the Lisbon treaty. It's British author, Lord Kerr, has suggested the clause is eminently reversible, but there's no precedent, as it's never been activated.
From a legal perspective, the task of revoking Article 50 would be a fiendishly complicated one. Although Britain took the decision to trigger alone, it can't do the same with any decision to call the whole thing off.
The powers vested in the Lisbon Treaty mean that, if Britain wanted to reverse Article 50, it would have to secure the backing of all other EU member states before it was able to do so. Many members would probably agree to this, given it's in their interests to keep Britain, a key trading partner and strong economy, within the bloc. But that's not to say a reversal would be unanimously approved.
A more realistic fail-safe might be an extension of the negotiation period, and the European Council certainly has the power to grant this, with the UK’s consent.
James McGrory, the co-executive director of Open Britain, is demanding that MPs be given a meaningful vote on the final deal negotiated with Brussels. He argues that if Britain gets a bad deal - or no deal at all - and MPs give the thumbs-down, we should definitely try and negotiate an extension with our counterparts in the EU.
He told talkRADIO: “Our elected representatives should have the ability to send Ministers back to the negotiating table if they do not think the deal on the table is good enough for Britain.
“If that requires an extension of the Article 50 talks, we should try to agree that with the EU.”
Yet this would obviously not equate to a full reversal of Article 50. For Remainers it would simply delay the apocalypse, rather than avoiding it.
If no extension is agreed before the end of the formal negotiating period, the UK will find itself out of the union. There'd be no chance to return to the negotiating table, and no chance to turn back on Article 50.
In fact the only way the UK could ever reverse Brexit would be to re-apply for membership, keeping in line with the “values of respect for human dignity, democracy, freedom, equality, rule of law, and human rights”, outlined in Article 2 of the treaty.
Again, it's debatable whether all 27 remaining EU member-states would be keen to have Britain back, given the country's public rejection of the EU and its values last year. But, for those who see Brexit as a nightmare and are looking for some way to end it, this might just be the only real option available.