This comes as Britain's new Brexit Minister Dominic Raab met for the first time with European Union chief negotiator Michel Barnier, with Mr Raab saying he is ready to work throughout August to "intensify" the talks and "get some energy" into them.
The EU is increasingly preparing for a no-deal Brexit scenario, as UK PM Theresa May looks weaker after pro-Brexit ministers' resignations from her cabinet.
He warned her plan - seen as a major concession by Brexiteers - for Britain to collect customs duties on the EU's behalf in order to maintain British-EU free trade in industrial and agricultural products may not be legally feasible, and that failing to submit the United Kingdom to a "common rulebook" on services as well as goods could lead to "unfair competion".
Barnier said the backstop arrangement in the final agreement will "not necessarily be ours" but he insists there must be one. "I'm sure in good faith, if that energy and that ambition is reciprocated, as I'm confident it will be, we will get there".
Barnier underscored the importance of settling the Irish border, saying "we can not afford to lose time on this issue and this is why we have invited the U.K.to work" on the issue next week.
She said she re-iterated in the meeting this morning that the Irish border requires a bespoke solution and needs "an absolutely worse case contingency plan" - i.e. the backstop agreement.
A senior British regulator also warned Britain's banks and insurers on Thursday to plan for a "hard" Brexit. 'At present, we can't exclude anything, ' Michael Roth, the State Minister for EU Affairs claimed.
The threat came after Michel Barnier, the EU's chief Brexit negotiator, questioned whether the Prime Minister's proposals were "workable" in his first response to the UK's white paper.
"It would lead to a fissure in relations which would be highly damaging for that great partnership that we have had for so many years, which has been so important in sustaining the worldwide order".
Brexit Secretary Dominic Raab has accused the European Union of "irresponsibly" ramping up pressure in withdrawal negotiations. Although, he added that many questions remain open.
May is due Friday to speak about Brexit in Belfast, after visiting the Irish border - one of the most hard issues facing Brexit negotiators.
May said the return of a hard border once Britain leaves the bloc would be "almost inconceivable", but dismissed the EU's current plan to avoid it as unacceptable.
Barnier's statement will have done little to assuage Breixteer concerns that the Prime Minister - who backed Remain during the European Union referendum - is saying one thing to the British public and another to the Brussels elite.
Connexion has interviewed the French Interior Ministry about how France expects to deal with British citizens after Brexit (with or without a "deal") for our August issue, published next week.
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