With Westminster and the rightwing press on a war footing, moderates in European council are desperate to restore trust

It is time for both sides in the Brexit crisis to calm down, according to EU officials. But after a week in which relations between Britain and its closest international partners have deteriorated further, fears are growing that the political holdalls once wielded by Margaret Thatcher in her fights with Brussels may be battered beyond repair.

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Even by the standards of past standoffs, the feud over how Britain will end its 44-year membership of the European club has spiralled out of control at breakneck speed. Since Theresa May’s decision to call a snap election to strengthen her negotiating mandate, critics in Brussels have raced to correct what they see as her misplaced confidence.

It was the decision last weekend by some within Jean-Claude Juncker’s cabinet to leak a damning blow-by-blow account of their frosty meeting to German newspaper Frankfurter Allgemeine Zeitung that sent the often strained relationship to a new low. Goading May in public before talks had begun properly in private was, several EU moderates have conceded, a “catastrophic mistake”: a provocation too good to ignore for a prime minister looking to rally the nation behind her. Detlef Seif, Angela Merkel’s Brexit spokesman, blamed the leak on a “babbling idiot”.

When May responded by accusing the EU of seeking to meddle in the British general election, it elicited a warlike reaction from London’s Eurosceptic press. “You can almost smell the panic gripping European elites,” thundered the Daily Mail’s editorial, while the Sun called those seeking to increase financial claims to a rumoured €100bn (£85bn) “infantile bullies”. The Daily Telegraph accused the EU of seeking “reparations” as punitive and perverse as those demanded of Germany after the first world war.

Charles Grant, the director of the Centre for European Reform lobby group in London, said: “The impact of the leak has been to strengthen hardliners in Westminster who want there to be no deal.

“Another consequence of the leaking is that the British government no longer believes that the commission is a credible or serious negotiating partner that can be trusted, and that is a real problem.”

But some believe this was no accidental escalation. Key Downing Street advisers are said to be convinced that opponents in the European commission are actively plotting to engineer a car-crash Brexit.

While such talk is fiercely denied by Michel Barnier and the rest of the EU’s Brexit negotiating team, it has been fuelled by his comments that Brexit can never be a success for Britain. A series of intemperate tweets from Guy Verhofstadt and individuals such as Martin Selmayr, Juncker’s chief of staff, only deepened the paranoia in Whitehall.

More moderate voices within the European parliament and European council, which represents national governments in Brussels, are desperately trying to restore trust on both sides.

The council president, Donald Tusk, said: “These negotiations are difficult enough as they are. If we start arguing before they even begin, they will become impossible. We must keep in mind that in order to succeed we need today discretion, moderation, mutual respect and a maximum of goodwill.”

As news of May’s speech came through on Wednesday, Ireland’s ambassador to London, Dan Mulhall, said: “Everyone needs to take a deep breath and calm down.”

But these are relatively minor voices compared with large countries and commission leaders and their already battle-scarred negotiators. Only after the German election could someone such as Angela Merkel perhaps be able to resume exerting a moderating influence.

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Grant said: “There isn’t really a sufficiently strong figure able to do that right now. Donald Tusk is generally liked and respected by most people, but he is a relatively weak figure. Nobody is scared of Donald Tusk. He is not someone who can easily knock heads together.”

Fears are instead mounting that the degree of bad blood will make future compromise all but impossible and strengthen the voices of those prepared to see Britain leave without a deal on money, trade or citizens’ rights.

A senior official in Brussels, fearing dire consequences for the four million EU citizens stuck on both sides of the widening gulf, said: “People are afraid. We must not allow them to become collateral damage in a pissing contest.”