SINCE the vote to leave the European Union in June 2016, the more optimistic among those on the losing side have been lobbying for a rematch. Some argue for a re-run on the basis that Brexiteers lied during the campaign and broke election law (on July 17th the Electoral Commission fined the official Vote Leave campaign £61,000, or $80,000, for deliberately exceeding spending limits). Others say the public deserves a chance to vote on the final deal, which will bear little resemblance to the glittering one they were promised. Yet the idea of a second vote has never taken off. Polls have shifted only slightly in favour of remaining, and there is no great enthusiasm for another plebiscite, which would be the fourth nationwide vote in as many years.

But the idea of revisiting the referendum is back in play. By law, Theresa May’s government cannot sign a Brexit deal without MPs’ approval. And in the past couple of weeks it has begun to look as if Parliament will reject any deal. The Labour opposition has set six tests for the agreement, which look designed to be unpassable. The Conservative Party, meanwhile, is in a rebellious mood. This week hardline Tory Brexiteers forced the government to toughen its approach to customs, before a faction of Tory Remainers forced it to soften its policy on medical regulation. More defeats were avoided by as few as three votes. It is hard to imagine MPs agreeing to the unappealing deal that Mrs May is likely to bring back from Brussels later this year. And if they don’t, Britain could crash out of the EU on March 29th with no deal at all.

Many in Westminster therefore wonder if the only way to break the deadlock may be to send the matter back to the people. One way would be with yet another election. Tory whips reportedly told their MPs that the government would call one over the summer if they defied it on key parts of its Brexit plan. But would Mrs May, election-flunker extraordinaire, risk it? Polls put Labour narrowly ahead of the Tories. In any case, a narrow victory for either party could leave Parliament in the same stalemate, since Labour is also divided over the best approach to Brexit.

So a second referendum is being proposed as a way to get a clear answer. On July 16th Justine Greening, one of Mrs May’s former cabinet ministers, proposed a vote with three options: stay in the EU; accept the deal that Mrs May agrees on with Brussels; or leave with no deal.

There are formidable obstacles to such a vote. Parliament would have to legislate for the referendum, which might be tricky if that same Parliament is against the Brexit deal that would be its subject. Labour says a referendum is “not its policy” and that MPs should sort out the mess. But it has left the door ajar: “To take [a second referendum] off the table completely, when there might be a set of circumstances where Parliament cannot deliver a meaningful vote, would be a mistake,” Tom Watson, Labour’s deputy leader, said on July 15th. The Scottish Nationalists would not oppose a second referendum; the Liberal Democrats would vote for one (provided they remembered to show up, as their leader failed to do at a vital Brexit vote this week). Mrs May has ruled out the idea—but of course, two years ago, she ruled out a snap election.

There would be little time to organise a new plebiscite. It took seven months to pass the bill for the original referendum. That process could be speeded up, especially now that Britain has a “here’s one I made earlier” template for such a vote, argues Eloise Todd of Best for Britain, which wants a second referendum. But it would almost certainly be necessary for Britain to ask the EU for more time. It would probably agree, believes Charles Grant of the Centre for European Reform, a think-tank, though it would hope to resolve matters before elections to the European Parliament at the end of May.

If all this could be done in time, what would be the question on the ballot? Britain has never had a multiple-choice referendum of the sort that Ms Greening suggests, though they are not unknown internationally. Finns were asked in 1931 if they wanted to scrap prohibition, maintain it, or remove it only for weak drinks (they overwhelmingly chose to abolish it). In 1977 Australians opted for “Advance Australia Fair” as their national song, from a line-up of four.

The difficulty is deciding how to pick a winner. Peter Kellner, a polling expert and Prospect columnist, notes that a single set of results could produce three possible winners, via first-past-the-post (picking the option with most first-preference votes), alternative vote (adding the second preferences of the bottom-ranked option to the tallies of the top two) or a Condorcet system (picking the overall winner of the three possible head-to-head contests). A poll last month for The Economist by YouGov, asking voters to rank hard Brexit, soft Brexit and Remain, returned exactly such a result (see chart). With a second referendum, “there is already potential for a crisis of democratic legitimacy,” notes Akash Paun of the Institute for Government, a think-tank. A complex vote with multiple interpretations would not help.