Jean-Claude Juncker and Donald Tusk say the door remains open for the United Kingdom to change course on leaving the EU. Talks of a second Brexit referendum have been quashed by Prime Minister Theresa May's office.
As EU negotiators kicked off preparations for the second round of Brexit talks, on Tuesday European Council President Donald Tusk urged the United Kingdom to rethink its divorce from the bloc.
"Brexit will become a reality, with all its negative consequences, in March next year, unless there is a change of heart among our British friends," Tusk posted on Twitter. "We here on the continent haven't had a change of heart. Our hearts are still open to you."
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While constitutional lawyers remain divided over whether the United Kingdom can withdraw its two-year notice to leave the EU, on Tuesday Prime Minister Theresa May reaffirmed her determination to follow through on Brexit.
"I think we've been absolutely clear, the British public voted to leave the European Union and that is what we will be doing," the spokesman for the prime minister told reporters.
As it stands, the UK is set to leave the EU in March 2019, beginning a transition period of a little under two years. Britain is scheduled to completely withdraw from the bloc on December 31, 2020.
The remaining 27 EU member states are expected to back a tougher set of terms for the next round of Brexit negotiations.
First, Brussels is expected to insist that the UK commit to all obligations during the two-year post-Brexit transition period, including accepting free immigration from the member states and remaining bound to the European Court of Justice.
Sources in Brussels have also implied that the European Union's chief negotiator, Michel Barnier, will also push the UK to allow EU citizens who arrive in Britain during the transition period to retain the same rights they currently enjoy.
Talks on a possible trade deal between the UK and EU, as well as how close London chooses to remain to the European single market and customs union, aren't slated to begin until April. However, Brussels has rebuked a lack of detail on behalf of the UK as reason for the painfully slow progress of the negotiations.
"What we need today is more clarity on the UK's vision," Tusk said. "The hardest work is still ahead of us, and time is limited."
Manfred Weber, the leader of the European People's Party group and a close ally of German Chancellor Angela Merkel's, said: "My message to London is: please don't complain anymore. Please stop complaining. Please deliver. Give us an outlook about what you want to achieve for the future relationship."