The meeting, on the sidelines of a European Union summit, had not previously been announced.
The British Prime Minister was due to address leaders of the 27 remaining EU states before they discuss Brexit in her absence at the European Council on Wednesday evening.
He said the President of the European Commission, Jean-Claude Juncker, would update leaders on the preparedness for all scenarios including no deal. Anyone hoping she was about to jet off to Brussels with the solutions that would break the Brexit deadlock will have been left fretting after this showing: the prime minister is floundering. "Only such proposals can determine if a breakthrough is possible".
An EU source said that the leaders had decided over dinner that they would not call a special Brexit summit as sufficient progress in the talks had not been made.
Mrs May won strong support from Cabinet colleagues as she set out two key "sticking points" preventing the conclusion of a withdrawal agreement.
Earlier, Irish Prime Minister Leo Varadkar said a longer transition period was not a substitute for an agreement on the so-called Irish backstop, created to prevent the need for customs checks at the border between Northern Ireland and the Irish Republic until a wider trade deal is done.
But despite intense speculation over a possible walkout, no minister at Cabinet indicated they might consider resigning from the Government over Brexit.
Repeatedly she failed to answer the hard questions on Brexit, on Chequers and on any divorce bill the United Kingdom might have to pay.
The prime minister failed to reassure MPs from the Democratic Unionist Party that there'd be no new regulatory checks between Northern Ireland and the rest of the United Kingdom after Brexit, and received a kicking from numerous pro-EU MPs, including up to 10 MPs who urged May to back another referendum.
Maybe - but it is unlikely to bring about the concrete agreement hoped for.
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According to the release, Canada Post will undertake age-verification check if a customer appears to be under 25 years old. You must be at least 19 years old to purchase cannabis in B.C.
Her official spokesman later told reporters: "The Cabinet strongly supported her on the importance of maintaining the integrity of the Union and agreed that we must ensure we can not be kept in a backstop arrangement indefinitely".
"Can the Prime Minister confirm what action the Government is taking to ensure this important sector for our economy continues to be able to access the workforce it will need?"
"We are all doing our jobs and we are trying to get the best deal for this country, and that's it".
Attendance at the demonstration is expected to exceed previous marches held in the capital as negotiations between Theresa May and European Union representatives near an end.
Labour MP Chuka Umunna, Lib Dem leader Sir Vince Cable, Tory MPs Sarah Wollaston and Anna Soubry and Green Party MP Caroline Lucas, are among the other supporter of the People's Vote campaign.
The attendees were Environment Secretary Michael Gove, Transport Secretary Chris Grayling, Chief Secretary to the Treasury Liz Truss, Foreign Secretary Jeremy Hunt, Attorney General Geoffrey Cox, International Development Secretary Penny Mordaunt, and perhaps most worrying for the prime minister, Brexit Secretary Dominic Raab.
Theresa May faces a Brexit showdown with restless Cabinet ministers on Tuesday morning.
In Luxembourg, foreign ministers from the remaining 27 European Union states were receiving a briefing from Mr Barnier at the General Affairs Council.
He said: "I think what's more likely is that dates will be suggested, but that there won't be a commitment to a new summit unless there is a signal from the negotiating teams that there is something to sign off on".