The PM in Belfast.

"To solve this point you have to be creative and listen to each other, and such discussions can and must be conducted", Merkel said at a news conference with Japanese prime minister Shinzo Abe in Tokyo.

"I think to extend simply because we hadn't reached an agreement would not provide any impetus for that agreement to be reached", said Fox, adding, "There is a big difference between if we had an agreement and we need some time to get the legalities done, that is one thing".

In the letter made public on Wednesday, Corbyn said the Brexit deal must include a "permanent and comprehensive" UK-wide customs union, a close alignment with the single market, "unambiguous agreements" on future security arrangements, and commitments on United Kingdom participation in European Union (EU) agencies and funding programmes.

In a meeting with her Cabinet on Tuesday, the Prime Minister told her team she would seek to push for changes to ensure the United Kingdom is not trapped in the insurance policy indefinitely.

She said she had had a "very direct meeting" with Mrs May.

She said her party has an "ongoing engagement" with the Government over Brexit. I saw the effect of the Troubles on our community and no one wants to go back to that.

Mrs May agreed to seek further concessions after MPs voted through an amendment in Parliament that demanded "alternative arrangements" to the measure.

The Irish Government accused the Prime Minister of harbouring unrealistic expectations over the backstop.

May raised the prospect of the World Cup returning to Britain for the first time since 1966 during a visit to Northern Ireland. Many Conservative MPs also look to the Unionist parties for guidance on this issue.

Unfortunately, the DUP and the European Research Group's narrative on the backstop dominates the debate, even though it is contrary to the feeling in Northern Ireland itself. The overwhelmingly positive impact of the European Union allowed normality to flourish in Northern Ireland in a way we could only have dreamed of in hard days gone by.

The government also outlined a role for Northern Ireland representation on the Withdrawal Agreement's arbitration committee on matters concerning the region.

"It is in that vein, in that light, that we are working with politicians across Westminster, across the House of Commons... with the Irish government and with the European Union - to find a way that enables us to maintain our commitments that we have set very clearly for no hard border".

The EU has repeatedly rejected the idea that the legal text of the Withdrawal Agreement could be reopened.

These include a drop in European visitors, border checks undermining the UK's status as a tourist destination, security and conservation risks to items on loan being held at the border for a long period, disruption to exhibition programmes, uncertainty about the future of export licencing regulation, and disruption to the supply chains that allow museums to remain open.

But asked how she could convince the people of Northern Ireland to accept a Brexit deal which was stripped of the backstop, Mrs May said: "I'm not proposing to persuade people to accept a deal that doesn't contain that insurance policy for the future".

At this critical juncture, Northern Ireland is represented only by the Democratic Unionist party, which is not representative of the people on Brexit - and so much more.

The Prime Minister's official spokesman told reporters in Westminster: "The conditions for a border poll are set out in the Belfast Agreement".