The controversial Brexit backstop has not been rewritten or “undermined” by new clarifications secured by Theresa May on Monday evening, the Irish prime minister has said.

Speaking in Dublin Leo Varadkar reassured the Irish media that the accords – presented by the British government as significant legally binding changes – were simply “guarantees and further reassurances to the United Kingdom of our good faith and intentions”.

“It does not reopen the withdrawal agreement or undermine the backstop or its application,” Mr Varadkar told the press, adding that “we’ve insisted that withdrawal agreement cannot be rewritten, and that the backstop agreement, while intended to be temporary, must continue to apply unless and until it’s replaced by future arrangements that can achieve the same objective – namely no hard border”.

But he added: “We’ve also said that we’d be prepared to offer guarantees and further reassurances to the United Kingdom of our good faith and intentions. Indeed we’ve offered such reassurances on many occasions.

“The instrument agreed yesterday puts those reassurances on a legal footing and represents an unambiguous legal statement of what has been agreed. It does not reopen the withdrawal agreement or undermine the backstop or its application.”

Britain Before Brexit: Northern Ireland Show all 12 1 /12 Britain Before Brexit: Northern Ireland Britain Before Brexit: Northern Ireland Derry, Londonderry A garage door displaying unionism, bolted shut, like a visual representation of Brexit Britain, locked to outsiders, safeguarding what’s inside Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry Rossville Street, the site of Bloody Sunday, where messages demand a severance with England. From this perspective, Britain is England in sheep’s clothing, the real empire, the centre of colonial power Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Bangor A political message in paint not yet dry, still forming, setting, adjusting, or in old paint finally eroding, melting away Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Bangor Moral judgement frames a residential view. The message seeks to make everybody involved in the religious narrative: those who don’t believe are those most in debt Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Castlerock The beach is sparse and almost empty, but covered in footprints. The shower is designed to wash off sand, and a mysterious border cuts a divide through the same sand Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast Two attempts to affect and care for the body. One stimulated by vanity and social norms and narratives of beauty, the other by a need to keep warm in the winter night Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast The gate to an unclaimed piece of land, where nothing is being built, where no project is in the making, where a sign demands the creation of something new Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry Under a motorway bridge a woman’s face stares, auburn and red-lipped, her skin tattooed with support for the IRA and a message of hostility to advocates of the Social Investment Fund Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry The Fountain Murals, where the curbs and the lampposts are painted the red, white, and blue of the Union Flag. A boy walks past in the same colours, fitting the scene, camouflaged Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Coleraine A public slandering by the football fields, for all to see or ignore. I wonder if it’s for the police or for the community Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast A tattoo parlour, where the artist has downed tools, momentarily, bringing poise to the scene, which looks like a place of mourning, not a site of creation Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry A barrier of grey protects the contents of this shop, guarding it from the streets outside, but it cannot conceal it completely, and the colours of lust and desire and temptation cut through Richard Morgan/The Independent

Mr Varadkar’s comments, pitched to his domestic audience that is worried about the strength of the backstop, are likely to be unhelpful for Theresa May, who is trying to present last night’s agreement as a major victory for UK negotiators that assuages the concerns of Tory MPs, ahead of a crunch vote on the plan today.

The Taoiseach said he hoped the House of Commons backed the agreement, and that the additions would ”eliminate doubt or fears, however unreal, that the goal of some was to trap the UK indefinitely in the backstop”. He said Brexit was a “dark cloud over us” that a positive vote this evening could remove.

The reassurances obtained by Ms May do not touch the actual withdrawal agreement, but instead take the form of other assurances by the EU that it will not seek to “trap” Britain in the backstop against its will. The fundamental functioning of the agreement has not changed, however – with the only legal way to escape the backstop permanently being negotiating a trade agreement that resembles membership of the single market and customs union.

The maths in Westminster is not on the government’s side, with some Brexiteers having already rejected the plan, arguing it does not address their fundamental concerns. These MPs do not want a permanent customs union with the EU, which they fear the backstop will become, and are worried about the imposition of checks on the Irish sea between Great Britain and Northern Ireland.

European Commission president Jean-Claude Juncker said in a joint press conference with Ms May on Monday evening in Strasbourg that there would be no “third chance” and that the EU would offer no further negotiations whatsoever.