Taoiseach Leo Varadkar has said he will raise the ruling on citizenship in the Emma DeSouza case with British prime minister Boris Johnson this week.
Mr Varadkar believes that British citizenship laws are out of step with the Belfast Agreement as he responded to Dáil questions about the ruling by the British Home Office that a woman from Co Derry is British by birth.
He said the Government would continue to uphold the provisions of the Belfast Agreement people in Northern Ireland have a right to be British, Irish or both and accepted as such.
"For that reason we continue to respect and confer people in Northern Ireland [with] Irish citizenship and with that comes citizenship of the EU" and all the rights that follow from that including the right to travel and work in the EU and in Britain and Ireland as though citizens of both.
He told Sinn Féin president Mary Lou McDonald that “we’re very much upholding our obligations in that regard in making sure that nobody in Northern Ireland is left behind regardless of which community they come from”.
Ms McDonald raised the long-running case of Emma DeSouza from Magherafelt which centres on her application for a residence card for her US-born husband Jake DeSouza.
The British Home Office won an appeal against an immigration tribunal that had upheld her right to declare herself as Irish without first renouncing British citizenship.
Mr Varadkar said the judgment “appears to make a distinction between identifying as British or Irish as opposed to being a citizen and that is a misreading in our view of the Good Friday Agreement”.
The Taoiseach said he had raised the issue with former British prime minister Theresa May and will do so again this week with prime minister Boris Johnson.
He said Mrs May had acknowledged the seriousness of the issue and pledged to review it. “We continue to actively pursue the issue” and the Tánaiste Simon Coveney would raise it with the Northern Secretary.
But Ms McDonald said that “simply raising the issue is not sufficient. We need a resolution to this matter and it needs to happen in a speedy fashion”. She called on the Taoiseach to insist that Mr Johnson move speedily to introduce legislation to address the issue.
The Dublin Central TD said Ms DeSouza had been "blackguarded and pursued through the courts by a very hostile and belligerent British system", despite the clarity of the Belfast Agreement and around her own Irish identity and citizenship.
Ms McDonald said the British system is “seeking to deny, frustrate and rob Irish and therefore EU citizens of their citizenship rights in the north of Ireland in a post-Brexit scenario”.
But the Taoiseach cautioned her against insisting and demanding change.
He told Ms McDonald “I know you’re suggesting a stronger approach that I insist and demand if that approach was effective you would be in government in Northern Ireland”.
He said “you raise things with people in a logical, respectful and consistent way. Insisting and demand is how you get nowhere and that’s why you got nowhere.”