The Irish taoiseach (prime minister) said the UK faced a strong and united EU who were prepared to back him up on his red lines – most notably the island’s border.
Speaking before he flew to Brussels for this week’s EU summit, the Irish leader promised a “strong message” for the UK and urged Mrs May to deliver more detail and clarity.
He said: “Time is running out for the Withdrawal Agreement to be concluded satisfactorily by the October European Council.
“I expect EU leaders to send a strong message to the UK that negotiations with the taskforce need to intensify.
“The lack of progress in the negotiations on the withdrawal agreement has been very disappointing.
“We still need to see detailed proposals from the UK on how it intends to deliver on the clear commitments it made in December and March.”
The UK Government has vowed to avoid a hard border between Northern Ireland and the Republic despite the former quitting the single market and customs union.
However Mrs May and her Brexit minister have failed to offer any workable proposal as to how this Catch 22 situation can possibly be squared.
Northern Ireland Secretary Karen Bradley has said the Government’s plan for ensuring “frictionless” arrangements will be proposed next month.
A backstop option, agreed in principle between the EU and UK, has been interpreted by Europe to mean Northern Ireland will stay in the bloc’s Customs Union if no other deal is reached.
However Mrs May declared early this year “no British Prime Minister can possibly agree” to terms which did just that, sparking accusations she had gone back on her word.
As far as Ireland is concerned, however, it is the EU’s word which holds the most power and importance.
Mr Varadkar said: “Ireland is grateful to our EU partners for their ongoing strong support.
“As President Juncker and President Tusk confirmed to me last week, if we don’t get agreement on a backstop, it won’t be possible to finalise the withdrawal agreement as a whole, including the transition arrangements.
“The European Council has stated on repeated occasions that nothing is agreed until everything is agreed.
“Meanwhile, our preparations and contingency planning continue in Ireland and are intensifying for all outcomes.”
The Taoiseach and his EU counterparts will also discuss how best to manage mass inflows of migration, which is likely to be another significant issue at the summit, along with the future development of the Eurozone, the EU budget and trade relations with the US.
Other topics include relations with Russia, security and defence, digital innovation, jobs, growth and competitiveness.