The European Union’s full devastating point-by-point rejection of Boris Johnson’s Brexit proposals for the Irish border has been revealed in documents obtained by the Guardian.

Leaked papers lay bare the scale of the multiple faults highlighted to David Frost, the prime minister’s chief negotiator, during the most recent talks.

The disclosure follows the prime minister’s claim on Monday that he had not yet heard the EU’s thoughts on the legal text tabled by Downing Street, under which a customs border would be reimposed on the island of Ireland.

Under the draft text, which the UK has not published in full, Northern Ireland would stay in the EU’s single market for goods and electricity if Stormont consents, giving the DUP a veto before the arrangement comes into force and then every four years.

The confidential report chronicling the latest negotiations reveals:

The British have been warned that the proposed Stormont veto provides the DUP with an opportunity to block the all-Ireland regulatory zone from ever materialising.

The proposals for a customs border were said to risk a major disruption of the all-Ireland economy. EU negotiators have pointed out that it has been rejected by groups representing Northern Irish business.

The UK is seeking a fallback of no controls, checks and border infrastructure, even if the DUP vetoes Northern Ireland’s alignment with the single market. The bloc’s internal market would be left wide open for abuse, the European commission has said in its rejection of the proposal.

The UK’s proposal leaves it up to a joint EU-UK committee to work out how to avoid customs checks and infrastructure near the Irish border once there are two customs territories and sets of rules on the island of Ireland, without offering a plan B if no such solution is agreed.

The UK has called for an overhaul of the common transit convention so as to avoid the need for new infrastructure in the shape of transit offices on either side of the border for the scanning of goods that have passed through multiple territories. Brussels has refused as it would lead other non-EU countries to seek similar exemptions, endangering the internal market.

The text affords what is seen as an unacceptable wholesale exemption for small and medium-sized businesses from customs duties and processes, but it fails to provide details on how to then combat smuggling.

On VAT, the British negotiators were told that the proposals fail to offer any solutions as to how to avoid payments and checks at the border.

Under the UK’s proposals all the state aid and level-playing-field conditions Theresa May agreed to in order to reassure the EU that Northern Ireland businesses would not enjoy a competitive advantage have been deleted. But Northern Irish firms would still be able to compete in the single market for electricity.

The UK would have access to an unlisted number of EU databases to allow it to police the customs border on the island of Ireland and the regulatory border between Great Britain and Northern Ireland. Whitehall would maintain such access even if the DUP vetoed alignment with the single market.

The EU’s hard-hitting rebuff was delivered to Frost on Friday and Monday, according to the leaked report, which was compiled after a briefing of EU diplomats by the commission.

The message had been passed on to Johnson in a series of phone calls with EU leaders over the weekend, during which Downing Street was left clear that the legal text did not form the basis for serious negotiation.

Following Monday’s discussions between Frost and the commission’s negotiating team, a UK government spokesman said it had offered the clarity that had been sought on the proposals.

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Frost is understood to be staying in Brussels on Monday night but the EU has not yet agreed to negotiate on the detail, given what sources described as the “fundamental flaws”.

The British government spokesman said: “Following hours of discussions last week, the UK provided additional legal text today. This provided further technical detail on customs and goods regulations to further clarify how the UK’s proposals would operate.”

Senior EU sources do not think Frost has any room for manoeuvre to change Johnson’s proposals. The European commission briefed member state diplomats that the UK had outlined “no new concepts” in a slightly revised legal text Frost offered on Monday.

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EU sources scoffed at claims coming out of Downing Street that a “counter-offer” could be expected from Brussels in the coming days. “It is the UK that wants to replace the backstop – and that is our solution,” said one senior EU diplomat.

On Monday, the Brexit secretary, Stephen Barclay, met with the Dutch foreign minister, Stef Blok, who tweeted: “Frank & honest discussion today with Steve Barclay. As good neighbours do.

“Important questions still remain on UK Brexit proposals and more realism and clarity necessary this week. Full support for Michel Barnier.”

An EU commission spokeswoman said the EU27 remained of the opinion that the UK had failed to offer an alternative to the Irish backstop, which would avoid a hard border by keeping Northern Ireland in the single market and the EU’s customs territory.

She said: “We all agree that we need a workable solution now and not something based on untried and revokable arrangements that would be left to negotiation during the transition period.

“The UK’s proposals do not meet at present the objectives of the protocol on Northern Ireland/Ireland and this is the shared view of the EU parliament but also all member states.”

The British government’s refusal to share the detailed legal text beyond the small circle of EU negotiators has infuriated diplomats and sowed confusion about the UK’s intentions on key points, such as the transition extension.

Under the current agreement the UK could extend the transition until the end of 2022, if both sides agree, but the UK is seeking to drop a reference in the Irish protocol to such an extension.

Some EU diplomats suspect the change is presentational, to match the government’s insistence it can get a speedy agreement on a future trade deal. The Guardian understands that the UK does not intend to drop the transition extension from the withdrawal agreement.