Irish citizens overwhelmingly backed moves to join the European Union in May 1972, with 83 per cent voting in favour on a high turnout of over 70 per cent.
Ireland first applied for EU membership in 1961 and again in 1967. The Accession Treaty followed a period of intense negotiations, which began in September 1970, and was widely endorsed by the public in a referendum two years later.
Marking the occasion at the start of this year, Taoiseach Micheál Martin praised the union for standing by them in aftermath of Britain leaving the bloc.
Martin said a young Irish State had “transitioned from relative economic stagnation and insularity” to a competitive economy at the heart of the single market.
Relationships “forged” between Irish and British government politicians at a European level “helped to develop mutual trust and understanding,” which assisted the peace process in Northern Ireland, he said.
Boris Johnson has today told the European Union there is no need for “drama” as he doubled down on hints he could override elements of his post-Brexit deal on Northern Ireland.
The prime minister said on Wednesday that the Good Friday Agreement is more important than the Northern Ireland Protocol, as he dismissed suggestions of any possible escalatory response from the EU as “crazy”.
He said the protocol fails to command support from unionists in the region, adding “we need to sort it out”, despite warnings from Joe Biden’s White House and European leaders not to single-handedly meddle with the agreement he brokered.
Foreign Secretary Liz Truss is set to tell the EU that the dispute over Northern Ireland cannot drag on, after warning she will “not shy away” from taking action as she accused the EU of proposing solutions that would “take us backwards”.
Related: Truss set to announce plans to rip up Northern Ireland Brexit deal
