On a sunny afternoon in Berlin’s Bergmannkiez neighbourhood, workers are moving boxes of mince pies, chocolate oranges and Christmas puddings into a soon-to-open shop.

For 24 years, Broken English used to be the German capital’s premier retailer of British delicacies and UK-themed souvenirs – until its owner threw in the towel at the start of this year: in interviews, she said she couldn’t face the hassle of having to fill in thousands of customs forms after Brexit.

Antje Blank, the shop’s new owner, is a German-born Anglophile with a Norfolk accent who couldn’t face the prospect of Berliners missing out on proper scones and thick-cut marmalade. She’s now stockpiling to make sure she can meet the cravings of expats and other lovers of British Christmas treats in case of a no-deal Brexit.

Blank is aware of the gamble she is taking: a nearby travel agency specialising in trips to the UK, she said, had recently shifted its focus on selling holidays to Ireland instead. She has already decided not to decorate the shopfront with a Union Jack: “The flag is too tied up with Nigel Farage, too tied up with anti-EU and anti-German feelings,” she said. “For a while, we considered hanging a Scottish flag outside.”

The frost that has descended on Anglo-German relations since the UK voted to leave the EU in 2016 has rarely felt as icy as it did last week. In a phone call on Tuesday morning, British prime minister Boris Johnson and German chancellor Angela Merkel reportedly failed to find common ground to avert a chaotic British exit from the EU, and even if the mood between Brussels and Westminster appears to have warmed a degree or two since then, the impact of the call and how it was handled afterwards will continue to make its mark in Berlin.

Dale Carr, the previous owner of Broken English. After running the store for 15 years, Brexit was the catalyst for her selling up in January. Photograph: Maurizio Gambarini/EPA

In a number of extraordinary briefings about the confidential discussion, a No 10 source said Merkel had demanded that Northern Ireland remain in a customs union with the EU “for ever”, making a deal look “essentially impossible, not just now but ever” to the UK side.

Reports of the call were pounced on by Brexit campaign group Leave.EU, which tweeted out an image reminiscent of wartime propaganda posters, saying: “We didn’t win two world wars to be pushed around by a Kraut,” next to a photo of Merkel with her arm aloft.

The image was accompanied by a line reading: “Angela Merkel’s demand that Britain leaves Northern Ireland to rot inside the customs union is reprehensible and shows the true colours of our supposed ‘European allies’.” Uncharacteristically, Leave.EU co-founder Arron Banks later apologised for the image.

Merkel declined to comment on the British accounts of the call, but behind closed doors, some German lawmakers and diplomats said they considered the read-outs of the call a major breach of protocol. “By publishing the contents of the call, whether they are true or not, Johnson is likely to have gambled away all his credit with the chancellor,” wrote her biographer Stefan Kornelius in Süddeutsche Zeitung newspaper.

While it is true that embarrassing details from the 2017 meeting of Johnson’s predecessor, Theresa May, with European commission president Jean-Claude Juncker were leaked to a German newspaper, Merkel’s chancellory is generally a leak-proof place, and her advisers are notoriously discreet in their dealings with the press. “She won’t forgive such a breach of trust, even if she probably won’t ever comment on it,” Kornelius wrote. “In 14 years as chancellor, she has certainly been rarely made such a spectacle of.”

Leave.EU’s Angela Merkel tweet following the leaked details of the Johnson-Merkel phone call. Photograph: Twitter/@arron_banks

The incident has prompted historians to reach far back into European history in search of comparable moments of diplomatic breakdown. Mareike Kleine, a political scientist at Berlin’s Freie Universität and the London School of Economics, said she was reminded of a famous incident in 1870, known as the “Ems dispatch”, when the French ambassador told Wilhelm, then king of Prussia and later Kaiser Wilhelm I, that Prussia should ditch its aspirations for the Spanish throne.

Wilhelm then gave the task of briefing the public with an account of the conversation to his chancellor, Otto von Bismarck, who deliberately cut out conciliatory language and dramatised the confrontational aspect, thus causing outrage on both the German and the French side.

“Bismarck wanted a hastened response from an enemy, who had overestimated his powers,” said Kleine. “His plan worked: the French launched themselves into a war they decisively lost, and in the process Prussia managed to bring the independent southern German states into the fold.”

Johnson’s chief adviser Dominic Cummings, suspected by many to be the source the source behind the leaks of the Merkel call, has in numerous expansive blog entries expressed his fascination with the ways the Prussian chancellor’s tactics “upended Europe”.

“But if someone in Britain really was trying to take a leaf out of Bismarck’s book, it didn’t work,” said Kleine. “Merkel didn’t rise to the challenge like the French did.”

Some historians fear the events of last week could mark a shift for the worse in Anglo-German relations.

“Two narratives have dominated the view of Germany in the Brexit debate,” said Helene von Bismarck, a Hamburg-based historian specialising in British foreign policy. “There are the good Germans who will come to Britain’s rescue during the negotiations, and there are the bad Germans who are pushing us around in Europe.”

“[Last] week Downing Street gave legitimacy to the second narrative, which was predominantly used by the extreme fringe of the Brexit debate. The briefing will further poison British perceptions of Germany, and will thereby harm the Anglo-German relationship.”

This is indeed a breach of trust, but it's not like Johnson had a reputation of being trustworthy before this happened Helene von Bismarck

As for the German reaction, said von Bismarck (a distant relative to Otto von Bismarck by marriage), “this is indeed a breach of trust, but it is not like Johnson had a reputation of being trustworthy before this happened.” The incident, she noted, had not gained as much attention in Germany as in Britain.

Richard J Evans, former regius professor of history at Cambridge University, agreed that Brexit has interfered with two strains of British thinking about its North Sea neighbours.

“Britain’s view of Germany has oscillated historically between two different models. On one hand, there was the ‘good Germany’ of Beethoven and Goethe, the land of poets and thinkers. On the other, there was the view of Germany as an aggressive threat: first economic, then military. In the 1970s and 80s, during the wide-ranging debate on the ‘decline of Britain’, the two images were briefly fused, when the British began to admire German efficiency in industry, holding up Vorsprung durch Technik as a motto to emulate, uncoupling it from the fear of Germany as a political power,” Evans said.

“But since reunification in 1990 the ‘bad Germany’ has dominated in the British mind again. Fear of German domination in Europe became a symbolic expression of euroscepticism, presenting a mythical image of Britain standing alone against Europe in 1940 and again in the 21st century.”

In turn, Evans said, Britain’s tortuous process of extracting itself from the EU has begun to change the German view of Britain. “Among German liberals, in the broader sense of the word, British institutions and qualities such as pragmatism and common sense have been held up as the more desirable alternative to the French revolutionary model since at least 1848. Brexit has thrown all that into question.”

At Berlin’s Broken English shop, Antje Blank remains optimistic that Tetley tea and Colman’s Mustard will sustain their appeal as political ties are strained. “There is still a large Anglophile community with a longing for rolling hills, Shakespeare and Jane Austen,” she said. “A lot of Germans think Britain has gone a little bit bonkers, but it will be all right in the end.”

• This article was amended on 14 October 2019 to correct Wilhelm’s title and the country’s name as at 1870: king and Prussia, not yet kaiser and Germany.