British Ambassador to the EU Tim Barrow hands the letter triggering Article 50 to Donald Tusk, 29th March 2017. Photo: European Union/Xinhua News Agency/PA Images The “second referendum” or, as some prefer, a first referendum on the deal, has become one of the key arguments of the Brexit debate. The political argument is fairly simple: the British people voted on whether or not to be members of the European Union, which gave a mandate to the government to negotiate the terms of exit. Given that those terms are unknowable at the outset of the negotiations, it is reasonable to check with the British people whether or not they are content with the deal on offer with a referendum at the end of the process. The counter-argument is also fairly simple: the people have spoken and decided they want to leave the EU. That is the end of the matter. The debate rages. But outside the political arguments, there is a little-known legal requirement for the government to hold a second referendum. The reasons for this are buried in the time of the coalition government, which in this febrile political age feels like ancient history. In 2011, long before any talk of an in/out referendum, the European Union Act was passed. This was one of David Cameron’s many attempts to manage the increasing Euroscepticism of his Conservative Party which reached its zenith in the 2016 referendum. The 2011 Act promised that no government would be able to amend or replace EU treaties without an Act of Parliament, and no law which would increase Brussels’ power over the UK could be passed without a referendum. Under the divorce agreement between the UK and EU, the proposed “implementation period” of Brexit runs from Brexit day (29th March, 2019) until December 2020 at the least. During that status quo phase, the UK remains subject to the rules of the European Union, such as free movement and the regulations governing the Single Market. But the UK is no longer a member of the organisation and no longer has a seat at the table or voting rights at the European Council. This situation was described as rendering Britain a “vassal state” by the prominent Eurosceptic MP Jacob Rees-Mogg. The agreement leaves Britain bound by the EU’s fishing rules but with no say in the quota it will receive. By any analysis, the transition deal involves Britain granting greater powers to the EU. Putting aside the political argument, there appears to be a legal requirement to hold a referendum on this transfer of powers. The big question has to be whether the 2016 referendum covers the requirement. There has been much debate about whether “the people” voted for Brexit knowing that they were voting to leave the Single Market, or the Customs Union, or the jurisdiction of the European Court, or Euratom. All this remains contested, with the narrowness of the referendum result (51.89 per cent voted to leave) further confusing matters. However, the prospect of a transition in which greater powers are granted to the EU and the UK’s powers reduced was clearly not part of any Brexit campaign. There is a lively campaign in favour of a “no-deal” Brexit—and much discussion of the World Trade Organisation option. The existence of this option, supported by the most vigorous proponents of Brexit, suggests that the transition period is debatable, not an inevitability baked into the original referendum result. There is still a powerful argument that the 2011 law was superseded by the 2016 referendum. Was the 2011 law put into place to deal with an issue that was fixed in 2016? If this were the case, it would have been easy for the government to repeal the 2011 law as part of the legislation establishing the 2016 referendum. One supporter of the 2011 law is Dominic Grieve QC, who said, “while alternative views on the meaning of the 2011 Act may be advanced it is entirely legitimate that this matter should be examined in court. Parliament provided for a referendum mechanism in the 2011 Act to ensure the public should be consulted on any significant EU treaty change. The terms of our departure and of transition are going to have major implications on our constitutional framework as and when they come into force.” As former Attorney General, Grieve’s potential support for the second referendum option is worth paying serious attention to. The 2011 Act can be repealed by parliament—but until that happens, it remains a law like any other. That means a second referendum has to happen.