Prime Minister Theresa May will call on the European Union to show “goodwill and determination” to avoid a disorderly Brexit, urging them to get behind Britain’s offer of a “fair arrangement”, a senior source said on Tuesday.

On the eve of an informal EU summit in Austria, May showed no sign of backing away from her Brexit plan, shrugging off criticism at home and in Brussels over her proposals for the future trade after Britain quits the bloc, the biggest foreign policy shift for the country in almost half a century.

The EU has called her Chequers plan, named after May’s country residence where a deal was hashed out with ministers earlier this year, a good starting point but has balked at her proposals for a future customs arrangement and Northern Ireland.

With just over six months before Britain leaves the EU, time is pressing and May is 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 recession.

A senior Downing Street source said she would repeat her message at a meeting of EU leaders in Salzburg on Wednesday and Thursday that Britain was proposing “a fair arrangement that will work for the EU’s economy as well as the UK’s”.

“To come to a successful conclusion, just as the UK has evolved its position, the EU will need to do the same,” the source said. “With goodwill and determination on both sides, we can avoid a disorderly exit and reach a deal that is in the best interests of both sides.”

While both sides have been making positive noises about the Brexit talks, there has been no deal yet over one of the biggest obstacles – how to meet their aim of keeping an open border between the British province of Northern Ireland and EU member Ireland.

Helping May

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

Earlier on Tuesday, EU negotiator Michel Barnier said the bloc was ready to improve its proposal for an “insurance policy” backstop arrangement on how to manage its Irish border.

May rejected a previous plan, saying it would effectively slice Northern Ireland away from mainland Britain.

The Downing Street source said she would again underline to EU leaders that “neither side can demand the ‘unacceptable’ of the other, such as an external customs border between different parts of the United Kingdom”.

Reiterating that Britain is committed to a “legally operative protocol on Northern Ireland”, the source said May would again underline that such an agreement must respect her country’s integrity, “which the Commission’s proposal does not”.

May would again try to reassure the EU that she is not trying to undermine its founding principles by opening a backdoor to its lucrative single market.

“Similarly, the UK understands that to the EU it would be unacceptable for us to seek the rights of EU membership without the obligations. That is not what we are doing,” the source said she would say.

“What we are proposing is a fair arrangement that will work for the EU’s economy as well as the UK’s, without undermining the single market.”