Austrian leader claims UK 'might discover Brexit not its best decision,' as EU chief warns unity will be tested 'more than ever' in next stage of talks

Austria's Chancellor called for Brexit to be reversed on Thursday, as the president of the European Council warned the next stage of talks would test EU unity "more than ever."

Donald Tusk, one of the EU's most senior officials, said securing the phase one divorce agreement with Theresa May demanded "courage, realism, but above all unity."

As EU leaders arrived at a summit in Brussels, Mr Tusk told reporters: "By the way, I have no doubt that the real test of our unity will be the second phase of the Brexit talks."

Meanwhile Christian Kern, the Austrian chancellor, claimed the UK might soon change its mind about leaving the EU as it faces challenges "not easy to solve."

"There will be a lot of tensions in the domestic political area in Great Britain," said the outgoing Chancellor before entering the summit, where EU leaders are expected to give the green light for trade talks begin.

"The Brexit discussion is not yet finished in the UK, they might be discovering that it wasn't the best decision for the country," he added. 

EU leaders' unified stance on divorce terms, such as the so-called Brexit bill, citizens rights and the Irish border, allowed them to exert considerable pressure over Theresa May during the first phase of talks.

But as the second phase of trade discussions opens, member states may begin to diverge as they scramble to protect their national interests.

Simon Coveney, the Irish foreign minister, has already indicated that his government hopes to be a "close friend" of Britain during phase two, as a good deal would be mutually beneficial.

Other member states such as France and Germany, however, privately hope to exploit Brexit as a means of enhancing their own financial services industries.

One key ally of Britain in the next stage of talks, Dutch prime minister Mark Rutte, was full of praise for Mrs May as he arrived at the summit.

“I still think she has a formidable stature here and last week Friday showed all of us that we should not underestimate Theresa May, she’s a formidable politician," Mr Rutte told reporters.

Asked whether the British prime minister could follow through on her promises, he said: "Yes, I do think so, because I believe in UK society and also in the political circles there’s widespread support for a reasonable negotiated exit of Britain from the EU.”

He went on to play down any damage wrought this week by Brexit secretary David Davis, who sparked a diplomatic row after suggesting the divorce agreement was not legally enforceable.

“An eyebrow was raised here and there because of that comment but I think it makes it more necessary to have as soon as possible that deal of last Friday in legally binding text so that we cannot have a misunderstanding exactly what was agreed," Mr Rutte said.

However, in a further blow to Mrs May, who suffered a bruising Commons defeat on Wednesday at the hands of Tory rebels, Luxembourg's prime minister warned there would be no time to renegotiate a second deal if the first were voted down by parliament.

"I really believe that to think that Theresa May will negotiate something, we will negotiate something and then again Theresa May will go back to Westminster is not good for the position of the negotiations," said Xavier Bettel. 

"This [negotiation] should be based on trust. I think Westminster should trust that Theresa May will do the best for the UK. Westminster shouldn't, even before we start negotiations to have in their heads that they don't trust the prime minister. I'm sure she's going to do a good job."

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