On Tuesday 24 January 2017, in his fourth month as negotiator, Barnier took the lift in the Berlaymont building to go up a few floors and meet Margrethe Vestager, the powerful Danish member of the Commission in charge of competition policy. The plan was to continue their discussion of 2016 on the level playing field. Most EU capitals made clear by then that this was a possible deal breaker. By the time Barnier reached Vestager's office, she had to cancel the meeting. He ran half an hour late. In the corridor before the lift, he had stopped to watch a dramatic proceeding live on the iPhone of an advisor, both mesmerized by the pronouncement of the UK Supreme Court's ruling in the Gina Miller case on whether the UK Parliament had to vote before the government could launch the exit procedure. The Court ruled against the argument that the British people had settled the question. It concluded that British constitutional law required Parliamentary approval before the government could notify Brussels. In the days before the ruling, media had speculated that the top UK judges could ask the EU Court if the EU Treaty allowed for revoking withdrawal after notification, but the Supreme Court judges decided based on British law only. This left a crucial question unanswered in 2017, namely whether a country could under EU law change its mind after notifying its withdrawal. That question had enormous consequences for the power balance of negotiations. It made a difference if the UK could test the waters on a deal with or without a looming cliff-edge, so it was no wonder the proceedings stopped Barnier in his tracks on his way to the meeting.

Existing models are inadequate

Vestager knew Barnier well as the former Danish minister of finance. In 2012, she chaired the Ecofin Council, the meeting of the powerful finance ministers, on behalf of the Danish presidency. Together, they failed to cajole George Osborne into supporting a cap on excessive bonuses for bankers, one of the very few pieces of EU law for which Barnier failed to enlist UK support when he was single market commissioner. Barnier reconnected with Vestager in his first days at work. After seeing Mark Rutte on 3 October 2016, he saw the urgency to kick-start the work on a level playing field.