May travels to Brussels without Ireland deal

The lunch is an "absolute deadline" set by the EU for the UK to come up with proposals on the three key divorce issues, so that EU leaders can give a green light on starting transition and trade talks at their summit next week.

However, the UK has rejected the deadline with a government spokesperson saying: "With plenty of discussions still to go, Monday will be an important staging post on the road to the crucial December Council."

Negotiations could possibly go on until Wednesday when Barnier will brief EU commissioners about the progress and make a formal recommendation on whether "sufficient progress" has been achieved for the next phase of talks to be unlocked.

Key divisions remain on the issues of the Irish border and the rights of EU citizens living in the UK.

Ireland, with the backing of the other 26 member states, wants the UK to provide guarantees on how to avoid a hard border between Northern Ireland – part of the UK – and the Republic of Ireland.

Dublin insists on clarity from the UK that there would be no divergence from EU rules in Northern Ireland.

Discrepancies in customs and standard rules could lead to the re-emergence of a border on the island, risking reigniting sectarian divisions that led to decades of violence which ended with the Good Friday agreement.

The UK however said it would not create a border between Northern Ireland and the rest of Britain.

Despite intense discussions over the weekend over the border issue, Irish officials said on Sunday night that "there is still a way to go."

"The Irish government remains hopeful, but at this stage it is very difficult to make a prediction," the official added.

European Council president Donald Tusk, showing support for the Irish position, said in Dublin on Friday that the EU will not accept any offer that Dublin is not satisfied with.

"If the UK offer is unacceptable for Ireland, it will also be unacceptable for the EU," he said after meeting Irish prime minister Leo Varadkar.

May will also meet with Tusk on Monday.

Citizens' rights

The issue of citizens' rights has also remained a hurdle.

"The 4.5m people who will be directly affected by Brexit will not be able to carry on with their lives as normal if the European Commission decides that 'sufficient progress' has been made on citizens' rights on Wednesday 6th December," said a statement of EU citizens living in the UK and UK citizens residing in the EU.

European Court of Justice oversight protecting these rights, such as family reunification, and free movement for UK citizens are key sticking points in the talks.

Juncker will meet with the European Parliament's Brexit task force led by liberal MEP Guy Verhofstadt a few hours before he welcomes May.

"We will not change our red lines. The lives of millions of families are at stake. If no clear commitment is made, the EPP group will not be ready to assess the progress made as sufficient to enter a 2nd phase of negotiations," Manfred Weber, German MEP and leader of the largest group, the European People's Party in the EP, tweeted.

The parliament needs to sign off the Brexit divorce agreement.

While for months a divorce settlement on financial issues between the UK and the EU represented the biggest hurdle to progress in talks, the UK last week mostly agreed to pay what the EU has been asking for.

But a failure to agree on the other issues and move onto the next phase of talks raises the risk of Britain crashing out of the EU in 2019 without arrangements on the terms of divorce or future relationship.

A new poll, published in the Mail on Sunday newspaper, showed that half of Britons support a second referendum on whether to leave the EU and a majority think the government may be paying too much money to the EU.