Britain agreed on Monday to the EU's timetable for Brexit talks, which states that sufficient progress must be made on divorce issues including citizens rights, the exit bill and Northern Ireland's border with the Republic before negotiations can start on a future trade deal. It was a clear rebuff to May's stated ambition of wrapping up a new free trade agreement quickly.
"I thought that was quite a good not concession, but certainly a good indication of the direction of travel of him as a negotiator". "They did vote to leave the EU. It's not the other way around". It's not about punishment, it's not about revenge. "The consequences are substantial".
Brexit negotiations begin after almost a whole year of speculation and build up. The clock is ticking down to midnight on March 29, 2019, when the United Kingdom will leave the European Union, with or without a deal.
The Brexit secretary David Davis had previously rejected this and predicted that it would be the "row of the summer" once negotiations began.
Barnier made clear on Tuesday that while there must be a first phase that excludes trade discussions, he does hope that four weeks of monthly negotiating sessions can get him to the point where he can ask European Union leaders in October to let him move on and discuss how the two sides can keep commerce open from 2019.
Davis said Britain hadn't backed down.
"We must think about the deep and meaningful partnership with Europe", he said. "This will be significant at the exit negotiations". But it must be done in a way that works for Britain. Their early priority will be to reassure the estimated 4.5 million European and British nationals living in each others' countries that they won't be forced to leave their homes or find new jobs after Brexit.
Adding to the complexity is Britain's current political situation, as May lost her Conservative majority in parliament after a snap election, sparking wide criticism of her leadership and worries about how long May and her cabinet would stay in power.
David Davis has conceded that trade talks will only begin after Brexit divorce proceedings.
"In a first step, we will deal with the most pressing issues".
The two negotiators already know each other well. They will use the time in between to work on proposals and exchange them.
"This first session was useful to start off on the right foot".
Michel Barnier, an enthusiastic walker, presented Mr Davis with a hiking stick while the Brexit Secretary gave his counterpart a book on trekking. After a private one-on-one meeting, the pair went to lunch with four senior officials, dining on Belgian asparagus, red mullet and meringue cake with strawberries. "There will be no hostility on my side".
Theresa May's personal position is also very weak, following a disastrous election campaign where she refused to participate in leader's debates and tended to appear before vetted sections of the public in highly managed events.