British Prime Minister Theresa May at a news conference during the EU Summit in Brussels on Thursday. REUTERS/Dylan Martinez LONDON — Imagine, by some miracle, that Theresa May and the Conservatives lose the June 8 general election.

Could a new government reverse its Article 50 request and undo Brexit?

The short answer is yes. But it would take a very, very unlikely series of events, given that the Labour Party is 21% behind the Tories in the most recent opinion polls.

Article 50 starts a two-year deadline ending in 2019, after which Britain will no longer be part of the EU, regardless of whether the UK has reached a trade deal with the rest of Europe.

Can a new prime minister take back the request to leave? Or is Article 50 an irrevocable act, ejecting Britain from Europe no matter what?

The law is unclear, but there have been a few clues from legal authorities as to whether Article 50 reversible.

Most recently, a leaked European Parliament draft resolution has said that the UK will be able to revoke Article 50 before it expires if the rest of the EU agrees.

That sounds tough — the UK would need 27 other countries to vote to let us back in. But in the scenario of a new prime minister who favours Remain, it would suit all parties just fine: It is highly likely that the other EU nations will welcome back the UK under the existing conditions of our membership.

But the issue has not been settled in the courts, not even the European Court of Justice. Here is what various legal authorities have most recently said:

THOSE SAYING ARTICLE 50 IS IRREVOCABLE:

Justice Secretary Liz Truss has said, "my understanding is that it is irrevocable." She made the claim on "The Andrew Marr Show." The official position of the government is that it would never undo its decision.

The UK Supreme Court, in its decision requiring the House of Commons to vote on a bill triggering Article 50, said, "In these proceedings, it is common ground that notice under article 50(2) (which we shall call 'Notice') cannot be given in qualified or conditional terms and that, once given, it cannot be withdrawn." That, however, was merely a procedural assumption in the case. The court did not rule on the merits of the position. As a matter of law it remains undecided.

THOSE SAYING ARTICLE 50 IS REVOCABLE:

The EU-27 Article 50 negotiators say: "... a revocation needs to be subject to conditions set by all EU-27 so they cannot be used as a procedural device or abused in an attempt to improve the actual terms of the United Kingdom's membership".

Lord Kerr, the author of Article 50, says "you can change your mind while the process is going on." He told the BBC: "During that [two-year] period, if a country were to decide actually we don't want to leave after all, everybody would be very cross about it being a waste of time ... They might try to extract a political price but legally they couldn't insist that you leave."

Speaking in the House of Lords this month, Kerr added: "When the government says as a matter of policy that they will not withdraw the notification ... they implicitly confirm that in law they could withdraw it and they could. It is revocable."

European Council President Donald Tusk suggested last year that Britain could change its mind. "In my opinion, the only real alternative to a 'hard Brexit' is 'no Brexit'" he said last October, adding that once exit discussions were over Britain must "assess the outcome of the negotiations and determine if Brexit is really in their interest."

The House of Lords was advised by its own legal counsel: "It is absolutely clear that you cannot be forced to go through with it if you do not want to: for example, if there is a change of government ... There is nothing in Article 50 formally to prevent a member state from reversing its decision."

All of this sounds wildly implausible right now. But it's worth bearing in mind that British politics currently consists of nothing but surprises. And two of the previously "unthinkable" conditions for reversing Article 50 have already happened: The government has called a new election and the Scottish parliament has voted for a new independence referendum.