DEFIANT Theresa May warned EU leaders that they were powerless to halt Brexit.

The PM told them there would be no second referendum and insisted that Britain would be heading out of the European Union on March 29 next year.

In a move that stunned No10, EU Council president Donald Tusk said her blueprint must be “reworked” just hours before she delivered a desperate pitch to leaders at a crucial summit of all 28 leaders in Austria.

She had hoped to pull off the most important 10 minutes of her Premiership at the Salzburg gathering by making a personal plea to the national bosses' faces to keep her Chequers plan alive.

The premature savaging was seen as a sign that hardline French president Emmanuel Macron and Germany’s Angela Merkel had triumphed over more sympathetic states such as the Netherlands, Austria and Hungary.

Instead, Mrs May was forced to tell her 27 other bosses over dinner: “We all recognise that time is short but delaying or extending the negotiations is not an option.

“I know that for many of you Brexit is not something you want.

“But it’s important to be clear that there will be no second referendum in the UK. The public has delivered its verdict, and as Prime Minister I will deliver on that. The UK will leave of 29th of March next year.”

EU chiefs’ hopes of delaying or even reversing Brexit have been bolstered by Labour leaders such as London mayor Sadiq Khan giving their backing to a second referendum – dubbed a People’s Vote.

Mr Tusk savaged the two most important parts of Chequers – a common rule book on goods and a new customs relationship - with a thinly veiled demand for more big concessions from the PM, and also over the Irish border.

But he kept open a thin thread of hope for Mrs May by also praising some other elements of her softer Brexit blueprint.

Declaring that the Brexit negotiations were entering “the decisive phase”, Mr Tusk said: “I’d like to stress that some of Prime Minister May’s proposals from Chequers indicate a positive evolution in the UK’s approach as well as a will to minimise the negative effects of Brexit.

"By this I mean, among other things, the readiness to cooperate closely in the area of security and foreign policy.

“On other issues such as the Irish question or the framework for economic cooperation the UK’s proposals will need to be reworked and further negotiated.”

The EU boss also issued another dire warning on how time was almost up, with just six months to go until Brexit day on March 29, saying: "Today there’s perhaps more hope but there’s surely less and less time.

“Therefore every day that is left we must use for talks.”

A deal must be cracked by the end of the Autumn, he added, and confirmed a final emergency summit would be held in mid November in the hope of sealing it.

And EU Commission President Jean-Claude Juncker also added to the pressure on Mrs May by saying that the UK and EU “are far away” from a deal still.

The long-feared for rejection comes just 10 days before the Tories’ turbulent annual conference begins – plunging Mrs May into a fresh confrontation with her angry party.

Hardline Brexiteer MPs and party members hate her Chequers blueprint, and even some of its supporters have insisted she must not concede any more ground to the EU.

Hitting back at Mr Tusk, No10 insisted Mrs May would not budge a further inch until she hears concessions from the EU first.

The PM’s official spokesman said: “What I heard from Donald Tusk is a welcoming of the evolution of the UK’s position and him setting out his plan for a special summit in November when he is hopeful a deal will be done.

“What this shows you is the EU is now ready to sit down and start to have a proper discussion on a future partnership.”

“The PM has evolved our position. It is now for the EU to evolve it’s position.

Earlier the PM joined Ulster Unionists MPs to throw out a fresh bid by Michel Barnier to set up a new customs border down the Irish Sea.

Issuing a new pledge to “improve” the EU’s offer to resolve the Irish border stand off, Brussels’ chief negotiator suggested clever technology could replace hard border post between Britain and Ulster.

But on her arrival at a summit of EU leaders at Salzburg, the PM said she still cannot accept any separation of the province from the rest of the UK.

The DUP’s Westminster leader Nigel Dodds also angrily shot down the Barnier plan, saying: “It still means a border down the Irish Sea”.

But Mr Dodds also dubbed it “progress of sorts” that Brussels is now ready to look at technological solutions, having already dismissed it a solution for the Ireland’s North-South border as “magical thinking”.

At the leaders’ dinner last night, Mrs May also warned them that there will be no Brexit deal unless their “unacceptable” Irish Sea border demands are dumped.

British diplomats hoped for warmer words from EU leaders over Chequers, at least until after the Tory conference in Birmingham.

Earlier yesterday, former Brexit Secretary David Davis warned the PM she would fail to keep Chequers on the table, as EU leaders will pile ever more demands for more concessions from.

Instead, Mrs May will be forced to “reset” and “step back to what Donald Tusk offered in March” - a Canada-style free trade agreement, Mr Davis argued.

Mr Davis told BBC Radio 4's Today programme: "All these things will come back and we'll see more and more pressure, and she will have a deal she won't be able to bring back to the House of Commons because it'll be lumbered with loads of other EU demands.

“So she's going to have to have something else."

The ex-Cabinet minister, who resigned in protest over the Chequers plan in July, also said he had repeatedly told Mrs May there would be a "pressure point" late in negotiations.

Mr Davis added: "It’s always the case with the European Union that they move at the last possible minute - after they've tested your mettle, after they've taken you to the cliff edge, and that's what will happen".