Let's get serious, EU tells UK

"We must start negotiating seriously," Barnier said, calling on the UK government to present its positions "on all separation issues."

He said the position papers that the UK government published earlier this month did not "remove ambiguity".

He also said that the EU would "not accept that separation issues are not addressed properly."

"This is necessary to make sufficient progress," he added, referring to the EU position that there will be no discussion on future EU-UK relations unless EU leaders agree at their summit in October that enough progress had been made.

The three main issues on which the EU27 wants progress are EU citizens' rights, the future of the border between Ireland and Northern Ireland, and the Brexit financial settlement.

For his part, Davis suggested that the EU was sticking to a rigid position and called on "flexibility and imagination from both sides".

It is "something I think the the Council asks for on some subjects," he noted in reply to Barnier's remark that the negotiation guidelines set out by the EU were "clear".

The UK government has argued in recent days that talks about the future, especially on trade, should start before the three main issues were settled.

It also said that how the Irish border will be managed will depend on the future relationship.

On Monday, the UK's Daily Telegraph reported that the EU "could be open to a Brexit climbdown over trade talks amid revolt led by France," prompting the French governmen to issue a denial.

In Brussels, Davis said that the "large number of papers" put out by his government covered important issues and that they were the "product of hard work and detailed thinking".

As Barnier said he was "ready to intensify negotiations," Davis replied that the Brits were "ready to roll up [their] sleeves."

Legal analysis

The current round of talks is likely to be a transition one before two others in September and October that will be crucial ahead of the October summit.

Officials noted on Monday that talks this week will be mainly technical rather than political.

The main sticking point will be the financial settlement.

Last week, British foreign secretary Boris Johnson admitted that the UK would meet its obligations but added that it will do so "as we understand them."

The UK government this week will present to the EU its legal analysis about the settlement but it will not publish a position paper on the issue.

The three working groups on citizens' rights, the financial settlement, and other issues will meet on Tuesday, Wednesday, and Thursday mornings. Discussions on Northern Ireland will be held on Wednesday.