Prime Minister Theresa May will press EU leaders on Wednesday to back her proposal for a "fair arrangement" on future ties between Britain and the bloc, call off "unacceptable" demands and show the goodwill needed to avoid a disorderly Brexit.

Before a two-day European Union summit starts on Wednesday evening, May showed no sign of backing away from her Brexit plan, shrugging off criticism at home and in Brussels over her proposals for future trade relations, the biggest policy shift for Britain in almost half a century.

She may arrive in Austria feeling more optimistic after the EU's negotiator Michel Barnier signalled he was ready to do more to address her concerns on Northern Ireland, which will have the only UK land border with the bloc after Brexit day.

But a British government source said London could not accept the province being separated off from the UK customs territory and Barnier's comments only got a hostile reception from a small Northern Irish party on which May relies on in parliament.

The summit opens in Salzburg with a leaders' dinner that has become a significant staging post in a carefully choreographed series of meetings with the EU before Britain leaves in March.

With just over six months to go, time is pressing and both sides are keen to secure some kind of deal before the end of the year and ease concerns over a disorderly exit, which could plunge the economy into a downturn.

Writing in Germany's Die Welt, May said the two sides were "near to achieving the orderly withdrawal that is an essential basis for building a close future partnership".

"To come to a successful conclusion, just as the UK has evolved its position, the EU will need to do the same.

"With goodwill and determination on both sides we can avoid a disorderly exit and find new ways of working together."

At the dinner at the spectacular Felsenreitschule theatre -- known to film fans for a scene in the musical 'The Sound of Music' -- May will make another pitch for support for her Chequers plan, named after her country residence where a deal was hashed out with her ministers earlier this year.

Then she will be out of the room on Thursday afternoon, when the other 27 leaders discuss her Brexit proposals.

EU officials said May could then meet Donald Tusk, the summit chairman, to be briefed on their talks. These are expected to end in an agreement on an extra summit in November to sign off on any deal that has been reached and a discussion of the scale of a declaration on future ties, which Britain wants to be as detailed as possible.

NORTHERN IRISH CONUNDRUM

While both sides have been making positive noises, there is no deal yet over what has become one of the biggest obstacles - how to keep an open border between the British province of Northern Ireland and EU member Ireland.

"On Brexit, it's very difficult. We have nothing on Ireland," Jean Asselborn, Luxembourg's foreign minister, told Reuters.

EU officials are minded not to paint May into a corner, aware that she faces increasing opposition to her plans in her Conservative Party and elsewhere, and needs a victory of sorts to persuade a reluctant parliament to back a deal.

Northern Ireland's Democratic Unionist Party, which backs May's minority government in Westminster, criticised Barnier's ideas for handling customs crossing the Irish frontier, saying they would still mean an unacceptable border between the province and the rest of the United Kingdom.

May has told lawmakers that they will vote either for a Chequers-based deal or to leave without an agreement. Mel Stride, a junior treasury minister, said pro-Brexit and pro-EU lawmakers could usher in a second referendum on EU membership if they reject her plan.

For now, against a frenzied political backdrop, it only benefits both the EU and Britain to keep the mood positive.

One EU official, speaking on condition of anonymity, said May's team had asked Brussels, and Barnier, not to say that "Chequers is dead" and that the bloc would highlight progress by talking about future ties.

"So we won't, we have Barnier trying to import parts of it - on security and cooperation on international affairs - to the declaration on post-Brexit ties. This is how we are trying to help her," the EU official said.

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