Theresa May’s plans for the Irish border post-Brexit were reportedly subjected to a “systematic and forensic annihilation” in Brussels – and remainers have seized on the news. 

According to the Telegraph, Brussels officials delivered “a detailed and forensic rebuttal” of the Prime Minister’s proposals to avoid a hard border with Ireland. 

Quoting unnamed EU sources, the report said Britain’s lead negotiator Olly Robbins was told at a high-level meeting in Brussels that “none of the UK customs options will work – none of them”.

May’s plan included three options for the Irish border, with Britain backing a close economic relationship that avoids customs checks or a technological solutions that would make the border near-frictionless.

In February, however, the EU published a version which only included the third “backstop” option, which effectively draws a customs border down the Irish sea – something May said would be “unacceptable” to any British PM.

Should Brussels reject the options put forward by May, it would be a major blow for the UK’s hopes of securing a Brexit deal. 

Pro-Remain groups have said the news is evidence the PM must step back from exiting both the customs union and single market. 

Colum Eastwood, leader of Northern Ireland’s SDLP, called for the Government to give a “cast iron guarantee” there would be no hard border.

He said: “It is now crystal clear that the British Government need to get their heads out of the sand. Theresa May can no longer try to ride both horses – on one hand reiterating her so-called commitment to no border in Ireland and on the other hand propose no workable solutions to prevent a border here. 

“The British Government must now move to the only sensible, credible and practical solution for preventing a hard border in Ireland and that is to retain full alignment with the customs union and the single market.

 “While those in Number 10 will no doubt be seeking to hide their blushes today as their proposals have been rubbished by Europe, now is not the time to run and hide. Now is the time for decisive leadership.”

Labour MP Stella Creasy, said May’s Brexit plans lie in tatters.

She said: “Just like David Copperfield in a Las Vegas courtroom this week, Theresa May’s magical thinking, in her case about the Irish border, has been fully exposed.

“No trickery is going to get her or her Government out of the hole they have dug for themselves in ruling out continued membership of the Customs Union and the Single Market.

“And, after a stinging defeat in the Lords earlier this week and every sign that the Commons will next week also back continued Customs Union membership, it is also clear that it is not just the European Commission who have no faith in her attempts at sleight of hand.” 

Creasy, who supports the People’s Vote Campaign, said the UK’s Brexit should go to a referendum.  

Labour peer Andrew Adonis added: “The Government is slowly waking up to the fact that the Brexit they have promised is not a Brexit that is possible. The EU has rejected their proposals on the Irish question because their proposals were fantasy with no basis in reality or in international law. This is a crisis of Mrs May’s making.”  

The SNP’s Stephen Gethins said: “We are just 10 weeks away from the crunch summit at which the Irish border issue was due to be settled – and less than one year away before the UK plans to leave the EU – yet astonishingly, the UK government has failed to deliver any meaningful solution.” 

He added: “There is clear momentum and political support for the UK to remain in the customs union.” 

The reports came as Britain’s former ambassador to the EU, Sir Ivan Rogers said that UK hopes of finding a technological solution to the border issue were regarded as “a fantasy island unicorn model” in European capitals.

A UK Government spokesman insisted that Britain was “continuing an intensive work programme to engage” on all the scenarios set out in the Joint Report agreed in December by Mrs May and European Commission president Jean-Claude Juncker.

The agreement included three options for the Irish border, with the British backing a close economic relationship which would make customs checks unnecessary or technological solutions to render them near-frictionless.

But a version published by the EU in February contained only the third “backstop” option, effectively drawing a customs border down the Irish Sea, which a furious Mrs May said “no British Prime Minister could ever agree”.

The report puts pressure on Mrs May ahead over a vote in the Commons next week on keeping the UK in the European Customs Union, just days after she was defeated on the issue in the Lords.

If the UK position is rejected by Brussels, the Government could be faced with a choice between remaining in the Customs Union or accepting a hard border in Ireland.

On Wednesday, European Council president Donald Tusk warned that there will be “no withdrawal agreement and no transition” without a solution on Ireland.

According to the Telegraph, Robbins was also warned that Brussels needs “full compliance” with EU rules on goods and agricultural products in the whole of the UK – not just Northern Ireland – if customs barriers are to be avoided.

A Government spokesman said: “We have been clear that we will protect Northern Ireland’s place in the UK internal market.

“That commitment was set out in December’s Joint Report which also includes our guarantee of avoiding a hard border between Northern Ireland and Ireland.

“As the PM’s letter to Donald Tusk said, we have made our position on aspects of the draft Commission Protocol clear.

“We have agreed that the areas covered in the draft must reflect those that meet our shared commitments.

“And we are continuing an intensive work programme to engage on all the scenarios set out in the Joint Report.”

Responding to the Telegraph report, former Treasury permanent secretary Lord Macpherson tweeted: “EU’s position on Irish border so predictable. UK sold pass by conceding ‘backstop’ in December, inviting EU to hold us to it. #badbusiness”