The Democratic Unionists have rejected fresh Government assurances on the Irish border backstop as “cosmetic and meaningless”.
Deputy leader Nigel Dodds said commitments from Downing Street had not altered his party’s strong opposition to Theresa May’s Brexit deal, while Sinn Fein also rejected Wednesday’s proposals.
In a 13-page paper, the Government pledged new domestic laws to assuage concerns that Northern Ireland would be treated differently to the UK if the Irish border backstop was ever enacted.
If the backstop is triggered, the Government said the Stormont Assembly and Executive would then be given a “strong” oversight role in its operation.
Mr Dodds said: “We reject the backstop, and have previously and consistently indicated we will not support an internationally legally binding withdrawal agreement that contains its provisions.
“Such an international treaty supersedes and overrides any contrary domestic legal provisions.”
He added: “The Assembly would not be able to override UK international legal obligations as the backstop provisions would be in the treaty.”
The backstop, enacted if a wider UK-EU trade deal failed to materialise, would see Northern Ireland continue to adhere to some EU rules.
It is designed to maintain a free-flowing Irish border regardless of the outworking of Brexit, but the DUP and other Brexiteers claimed it would undermine the constitutional integrity of the UK by creating barriers between Northern Ireland and Great Britain.
The Government has offered a legally binding commitment to “consult” with Stormont before deciding to either enter the backstop or ask for an extension of the implementation period, due to expire at the end of 2020.
If the EU proposed changing any laws that impacted the operating of the backstop, the Government said it would have to consent to such a measure applying to Northern Ireland.
It has now committed to seek the agreement of the Assembly for any such changes.
However, the ultimate decision would be taken by Parliament.
Sinn Fein also rejected the proposal to give the Assembly a role, claiming it would hand the DUP a “veto”.
Mr Dodds highlighted that the EU-UK Joint Report on Brexit in December 2017 contained a commitment that the Stormont Assembly would ultimately decide if specific Northern Ireland arrangements would be required.
He said: “Consultation cannot replace the Assembly determining these matters.”
Wednesday’s proposals would be insufficient to address “major and significant” flaws in an internationally binding backstop with no exit mechanism, he added.
Sinn Fein president Mary Lou McDonald said the draft Withdrawal Agreement cannot, and will not, be rewritten, renegotiated or vetoed by Westminster or the Assembly.
She added: “Furthermore, no British government can unilaterally limit the role and function of the North South Ministerial Council or rewrite the Good Friday and other agreements.”
The Assembly has been in cold storage for almost two years following the collapse of the last Sinn Fein/DUP-led powersharing administration.
If it was to be resurrected, the institution’s voting structures mean large groupings of unionist or nationalist Assembly members can effectively wield a veto – using a device called the “petition of concern” – even if a majority of other MLAs are in favour of a particular course of action.
Ms McDonald met chief EU Brexit negotiator Michel Barnier in Brussels on Wednesday and said the DUP was out of step with majority opinion in Northern Ireland on Brexit.
Nationalist SDLP leader Colum Eastwood said: “The British Government’s latest ‘commitments’ to offer Northern Ireland an opportunity to provide consultative advice on backstop provisions is nothing more than an empty veto being handed to an empty chamber; an attempt no doubt to appease the DUP, and a tactic that has once again failed.”
Brexit minister Chris Heaton-Harris said there would be no immediate changes on the border between Northern Ireland and the Republic in the event of no deal.
“Initially on day one, the differences are not going to be that great but there could be divergence in tariffs further down the line.”