Angela Merkel is likely to give a friendly but firm rebuttal to Boris Johnson during his first overseas visit as prime minister on Wednesday, with politicians and officials in Berlin saying they do not consider that his letter to Donald Tusk asking the EU to drop the Irish backstop contains constructive proposals for further negotiations.

“The letter to the president of the European council is not a serious offer, and Boris Johnson knows it,” said Norbert Röttgen, an ally of the chancellor who heads the German parliament’s foreign affairs committee.

In a four-page letter published on Monday night, Johnson called on the EU to scrap the backstop, calling the last-resort solution for a seamless border on the island of Ireland anti-democratic and “inconsistent with the sovereignty of the UK as a state”.

The British prime minister’s first official proposal to the EU since taking office last month has been met with responses ranging from indifference to incredulity in the German capital, with senior officials saying it showed Westminster’s debate on the withdrawal agreement to be stuck on the same arguments of the so-called Brady amendment, which the EU rejected in January.

“The British prime minister starts his letter by saying he is personally committed to finding an agreement, but there is no sign in the rest of the letter that this is actually the case,” said Röttgen, a delegate for the conservative Christian Democratic Union (CDU). “To suggest the backstop could weaken the Good Friday agreement – that’s strong stuff.

“If Johnson really wanted to achieve something on his visits to Paris and Berlin, he would have been well advised against writing this letter.”

Johnson will receive military honours outside Angela Merkel’s chancellory at 6pm CET on Wednesday, followed by a meeting in which the two leaders will discuss bilateral and European policy issues.

“Merkel is politically and emotionally well inclined towards the British, and her willingness to maintain friendly relations between the two countries will be on display on Wednesday,” said Röttgen. “But the extent to which the Johnson government is prepared to humiliate itself for a trade deal with the USA has not gone unnoticed in Berlin.”

A failure to reach an agreement over the terms of Britain’s departure from the European Union would lead to the UK crashing out of the bloc on 31 October.

On the surface, Merkel’s government has been projecting a confidence that it is in a better position to cope with a chaotic no-deal scenario than the United Kingdom. “An exit without a deal would be in no one’s interest,” a spokesperson for the chancellor said on Monday. “But we are prepared for all eventualities that a disorderly Brexit would bring.”

The German government has passed more than 50 laws and transitional arrangements for the eventuality of a no-deal Brexit at the end of October, and some concerns, over the UK-reliant process for licensing blood reserves for example, have been alleviated since the original exit date in March.

Legislation has been prepared to ensure British people and their family members living in Germany will receive residence permits if the UK leaves the EU without a deal, irrespective of the Home Office’s latest plans for EU citizens in the UK.

Behind the scenes, however, there are concerns that the potential crises emerging from a hard Brexit are too complex to be adequately prepared for, and that Germany’s export-focused economy could be fatally hit at a time when it is already being squeezed by a trade war between China and the US.

Even before Brexit has happened, German exports to Britain are down 4% year on year, according to Commerzbank’s figures, making it no longer the country’s third-biggest export market but the fifth.

Yet the current consensus in Berlin is that the time to address such economic concerns in negotiations with Britain has already passed.

“I don’t see any sign of Germany having changed its position on the backstop since Johnson has come to power,” said Nicolai von Ondarza, a political scientist at Berlin’s SWP thinktank. “The official line remains the unofficial line.

“What has changed is the credibility of a no-deal Brexit. But there is no room for Germany to change its position. If the EU gave in to Johnson’s hardline course now, it would send a signal not just to London but the rest of the world. This is not just a negotiation between Britain and the EU, but one watched by the whole world, including the US.

“If Germany and France gave in now, it would send the fatal signal that the two biggest members states are willing to sell out smaller states for short-term economic interest.”