FIRST came economic and political turmoil after the Brexit vote. Now, inevitably, come the lawyers. Mishcon de Reya, a London-based law firm, backed by David Pannick, a senior barrister, is preparing a court challenge to claim that the government cannot lawfully invoke Article 50 of the Lisbon treaty, which allows a country to leave the European Union, without a formal act of Parliament. One theory is that such an act might be blocked in one or both parliamentary chambers, since both have a pro-Remain majority.

The argument is, first, that the June 23rd referendum was not legally binding, which is correct. But second, Mishcon de Reya and Mr Pannick assert that, once Article 50 is invoked, it may lead within two years to formal Brexit without any further parliamentary action. That would contradict the 1972 European Communities Act, which gives supremacy to EU law: hence the need for a new act. Yet most constitutional experts disagree. Foreign policy has always been a matter of royal prerogative, exercised by the prime minister or foreign secretary. Martin Howe, another senior barrister, insists that the Brexit referendum vote not merely permits, but mandates, the invocation of Article 50, without the need for any further parliamentary vote.

As so often, political reality will trump the lawyers. Alan Renwick of the UCL constitution unit argues that there is now a political imperative for the next prime minister to hold a parliamentary vote before the invocation of Article 50. But it is hard to imagine that MPs would choose to overturn the majority decision of the referendum on June 23rd. The real issue is exactly when the article should be invoked.

Theresa May, the home secretary and front-runner in the Tory leadership contest, who backed the Remain side in the referendum, wants to put it off as long as possible, to give the government time to work out its negotiating stance and have preliminary talks with Britain’s EU partners before setting the clock ticking. Andrea Leadsom, the pro-Leave candidate who is emerging as her most likely rival for the leadership, wants to invoke the article sooner, to speed up the Brexit process.

In the end, whoever wins is likely to be cautious about an early resort to Article 50. Once that is done, it not only sets a two-year deadline, but also hands most of the bargaining power to the other 27 countries, which get to agree on the terms for Brexit without Britain having a veto over them. Yet delay, while sensible, has problems of its own. It looks like shilly-shallying after a clear referendum result. And other EU leaders are likely to insist that there can be no formal negotiations until Article 50 is invoked, precisely because it gives them greater leverage.

Moreover, if the formal process is delayed, as Ms May has suggested, until the end of the year or even into early 2017, it will fall slap in the middle of heated campaigning for the French presidential election next spring. The Netherlands, Germany and (probably) Italy are also heading for tricky elections next year. Domestic political considerations will make it even harder for other EU leaders to be helpful to the next British prime minister, whoever he—or, almost certainly, she—is.