Boris Johnson’s hopes of entering into intensive and decisive Brexit negotiations next week could be dashed after he was sharply criticised in Dublin, Paris and Berlin for signalling plans for the return of a hard border on the island of Ireland.

The prime minister is expected to set out his long-awaited proposals for the Irish border in his speech at Conservative party conference in Manchester on Wednesday, outlining what he will call “a fair and reasonable compromise” but warning that if the EU27 does not engage, he will press ahead with no deal.

Johnson confirmed on Tuesday that his plans would include a customs border on the island of Ireland but insisted the proposals would show that the new regime of checks and controls would be light-touch.

The plan would also involve Northern Ireland staying under EU single market regulations for agrifood and manufactured goods for four years, leaving it in a special relationship with the bloc until at least 2025.

Stormont will at that point decide whether to continue alignment with EU standards on manufactured goods or follow UK rules as the country diverges.

Brexit: Boris Johnson to offer EU 'far-reaching' alternative backstop plan - live news Read more

But the plans in which Northern Ireland would have two borders for a four-year period are set to receive a frosty welcome when they are formally published on Wednesday.

If the UK had accepted the need for Northern Ireland to temporarily stay under both single market regulations and in a shared customs territory with the EU after Brexit, sources in Brussels disclosed to the Guardian that pressure might have been applied on Dublin to accept a time limit, an unthinkable concession just six months ago, and one yet to be discussed among the EU27.

But officials and diplomats said the current “kamikaze” approach taken by Downing Street to the customs border offered no way forward and Johnson’s hopes of finding an agreement would be swiftly dashed. “I expect Mr Barnier [the EU chief negotiator] will make it clear very quickly that this does not stack up,” said one EU diplomat.

With little over two weeks before the crunch EU leaders’ summit at which Johnson hopes to sign off on a deal, Downing Street is banking on then entering secretive “tunnel” negotiations to hammer out the details of an agreement.

Johnson’s predecessor at No 10, Theresa May, had secured an all-UK customs element to the backstop following such a period of talks in 2018, during which the European commission’s negotiators took risks over the unity of the EU27 in order to find a deal that could be put to parliament.

When that deal emerged from the secret talks, a number of member states, including France, were unhappy with the outcome but allowed it to pass, having been convinced it was the only deal the Commons could accept.

But the UK’s current direction of travel, including an insistence on the return of a customs border on the island of Ireland, offered little room for negotiation, EU diplomats said. “I haven’t seen a tunnel and I have never even seen the signs of heading to a tunnel,” said one EU diplomat. “Please put on your lights. I think it is a bit premature.”

Q&A What is a Northern Ireland-only backstop? Show Hide The British government’s version of Brexit involves the UK ultimately leaving the single market and customs union, requiring the return of a range of checks on goods crossing the border between Northern Ireland and the Republic of Ireland. The “backstop” is intended as a standstill placeholder to ensure such checks do not have to be imposed between Brexit happening with a deal, and the start of a new free trade agreement yet to be negotiated between the UK and the EU. Theresa May's withdrawal agreement proposed keeping the whole of the UK in a shared customs territory with the EU during this period. An alternative idea involves only Northern Ireland staying in the EU’s customs territory. That would place a customs border in the Irish Sea. May described it as a threat to the constitutional integrity of the UK, but the new prime minister, Boris Johnson, has opened the current talks by proposing an all-Ireland agri-food zone. The suggestion is that he will seek to quietly build on that with further NI-only arrangements. Given an NI-only backstop was an EU proposal in the first place, the U-turn would be warmly welcomed in Brussels, although attempts to give the Northern Ireland assembly a veto on its continuation would not be acceptable, and the DUP would be unlikely to support the prime minister in such a move in parliament. If there is a no-deal Brexit, then there is no backstop. Daniel Boffey

Speaking to the media on Tuesday, Johnson denied reports that his first formal proposals to the EU would involve customs clearance sites five to 10 miles from the border to the north and the south to deal with imports and exports.

The prime minister reiterated, however, that Northern Ireland could not be left in the EU’s customs territory after Brexit and said it was simply a “reality” that there would need to be extra checks and controls on the island of Ireland.

Speaking in the Irish parliament, the taoiseach, Leo Varadkar, welcomed the fact that Johnson had “disowned” the reported contents of the “non-papers” discussion documents submitted by the UK to the European commission but fired a shot across the prime minister’s bows.

“I’m conscious when answering your question that I am talking about non-papers that I haven’t seen,” Varadkar told the Irish parliament. He added: “I very much welcome Boris Johnson’s words today when he disowned the non-papers. Had he not, in my view it would be hard evidence of bad faith by the UK government.

“The UK government promised no hard border or associated controls or checks and we expect the British government to honour that promise made in the withdrawal agreement. People here don’t want a customs border between north and south and no British government should seek to impose customs posts against the will of the people on the island of Ireland.”

Quick guide Why is the Irish border a stumbling block for Brexit? Show Hide Counties and customs Inside the EU, both Ireland and Northern Ireland are part of the single market and customs union so share the same regulations and standards, allowing a soft or invisible border between the two.

Britain’s exit from the EU – taking Northern Ireland with it – risks a return to a hard or policed border. The only way to avoid this post-Brexit is for regulations on both sides to remain more or less the same in key areas including food, animal welfare, medicines and product safety. The 'backstop' in Theresa May's Withdrawal Agreement was intended to address this - stating that if no future trade agreement could be reached between the EU and the UK, then rules and regulations would stay as they are. This has been rejected by Brexit supporters as a 'trap' to keep the UK in the EU's customs union, which would prevent the UK striking its own independent trade deals. There are an estimated 72m road vehicle crossings a year between Northern Ireland and the Republic of Ireland, and about 14% of those crossings are consignments of goods, some of which may cross the border several times before they reach a consumer. Brexit supporters say this can be managed by doing checks on goods away from the border, but critics say it will be difficult to police this without any physical infrastructure like border posts or cameras, which could raise tensions in the divided communities of Ireland.

Interactive: A typical hour in the life of the Irish border Photograph: Design Pics Inc/Design Pics RF

The chair of the Bundestag’s foreign affairs committee, Norbert Röttgen, who is in the same party as the German chancellor, Angela Merkel, tweeted: “Johnson simply doesn’t learn: his latest Brexit plans are not serious and violate the law. He wants to ask not to extend the deadline and proposes a backstop that de facto is a hard border. Not least to protect the sovereignty of parliament. EU should give a long extension.”

In a sign of widespread dismay at the British government’s choices, France’s foreign minister, Jean-Yves Le Drian, said a no-deal Brexit was now the most likely outcome. He said: “You know France’s position. It considers that the withdrawal agreement is the best solution. But today the most plausible scenario is an exit without a deal.”