EU chief Brexit negotiator Michel Barnier Michel Barnier looks on during a home affairs council debate on December 12, 2017 in Brussels | Emmanuel Dunand/AFP via Getty Images Michel Barnier: Full trade deal impossible by Brexit date His comments contrast with those of David Davis, who said at the weekend he expected a ‘substantive trade deal’ to be struck before the UK’s exit date.

By the time the U.K. leaves the European Union it will only be possible to draw up a "political declaration" on the future framework for trade with the bloc, not a full trade deal, the EU's chief Brexit negotiator Michel Barnier said Tuesday.

Speaking at a press conference after a meeting of foreign affairs and EU ministers in Brussels, he said there is not enough time to do anything more detailed, but also that agreeing a full trade deal would be prevented by legal and technical constraints.

His comments were in stark contrast to those of the U.K. Brexit Secretary David Davis, who told the BBC's Andrew Marr program on Sunday that barring "minor tinkering" by the time of Britain's exit date of March 2019, "we would expect the substantive trade deal to be struck." He said that the formality of signing would need to happen “one minute, or one second, after we leave."

Barnier said it would be possible by October next year to reach a draft withdrawal treaty to be ratified by the European Parliament and national parliaments ahead of the formal exit date of March 29, 2019.

"[This treaty] will be accompanied by a political declaration ... which will describe the framework for our future relationship, a political declaration, but it cannot be anything else, in technical, legal terms it is simply not possible to do anything else," he said.

“So we'll need more time and that's why the transition period can come in useful, to begin and conclude a negotiation on a free trade agreement, but we'll need more time,” he added.

He also suggested that the Brexit secretary was being willfully optimistic. "[Davis] has experience of European matters, we were ministers of European affairs at the same time ... and he knows perfectly what is possible and what is not possible,” Barnier said.

On Friday, EU leaders are expected to sign off on a political agreement reached last week between Prime Minister Theresa May and Commission President Jean-Claude Juncker on the first phase of the talks — known as the joint report. In the same BBC interview, Davis suggested that the agreement was not legally binding, although he later rowed back from the comments.

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But Barnier said: “[The EU] will not accept any backtracking from the U.K on commitments. In the joint report, all our points of agreement are now closed.”

“First we need to ensure that the joint report is translated into legally binding and precise language for the withdrawal agreement,” he said.