I T BEGAN AS a demand from a handful of Liberal Democrat MP s and a hard core of fervent Remainers. Now it seems to have the support of half the country. As the government’s Brexit plans fall apart, a second referendum has come to look ever more likely. But how would it work in practical terms?

The main dilemma is what to put on the ballot. Some supporters of a “People’s Vote”, such as the Conservative MP Justine Greening, back a three-way poll. Voters would rank their preferences, with a choice of remaining in the EU , backing the government’s deal or leaving with no deal at all. Others, including the “People’s Vote” campaign, would prefer a binary choice between staying and leaving. A third option is a two-stage referendum. Voters could be asked first whether they want to leave the EU , and only if they still do by what method.

Each option has problems, point out academics at University College London, as well as taking time to organise. A binary choice might bring accusations of unfairness. Remainers would not wish to choose only between the government’s deal and no deal, for example. A straight choice between three options, with the most popular declared the winner, would also be tricky. One option could win with just 34% of the vote, which might not seem a decisive answer. If two options involved leaving the EU , Brexiteers might argue that the Leave vote was split.

Britain could use an alternative vote ( AV ) system that considers people’s second choices. But though some places use preferential voting for local elections, a three-way choice with AV is unfamiliar to most voters, requiring a public-information campaign. Two rounds of voting are also unfamiliar.