The Greens in Ireland have accused European chiefs of breaking their own competition rules and the Government of turning a blind eye over the go-ahead for the new Hinkley nuclear project.
Located 241km from the Irish coast, the planned facility has been examined by watchdogs in Dublin for potential environmental risks which found "routine operation" would have no measurable radiological impact on Ireland or its seas.
Eamon Ryan, Green Party leader who lost his parliamentary seat at the last election, said the European Commission sign-off allows electricity to be generated at Hinkley at twice the price of alternative renewables.
"The decision supports an uncommon market, which brings us back to a highly centralised energy model and hinders the development of a cleaner, safer and more efficient energy future for everyone," he said.
"The Irish government have turned a blind eye to the dawning of this new nuclear age in Britain.
"There is no accounting for the security risks that come with the building of such a plant, and no apportioning of the massive clean-up costs that will come when the plant has to be decommissioned."
Mr Ryan called on Environment Minister Alan Kelly to explain what action the Government intends to take over the development of Hinkley.
The Department of the Environment in Dublin said they had not received a full written report from Brussels on the state aid ruling.
"When these details are received they will be examined and a decision will be taken as to what action, if any, is required to be taken by Ireland. Matters in relation to State Aid are generally a matter for the of Department of Finance," a spokesman said.
Michael Moynihan, Fianna Fail spokesman on natural resources, called on Taoiseach Enda Kenny to state if he made any representations to Prime Minister David Cameron on Hinkley.
"Ireland needs to robustly defend its interests here. We cannot stand aside and watch Britain potentially build another harmful nuclear power plant, which could have a devastating environmental impact on the Irish Sea and on the Irish East Coast," he said.
The department also said there is close contact with the British government on all their nuclear concerns - environment, management of radioactive waste and the rationale for new facilities.
Ireland's radiation watchdog in 2013, examined five scenarios from a nuclear accident at UK sites and found the less likely the accident, the greater the impact in Ireland.
It pointed to the potential for food controls and farm protection from any scale of accident to ensure food was safe to eat and i n the worst case scenario, a one in 50,000 event, people would be forced into bunkers or shelters.
It said, for people living in Ireland, a large release of radioactivity into the Irish Sea on the scale of Japan's Fukushima would be lower than the annual radiation dose limit.
It examined weather patterns for 21 years and said radioactive contamination in the air would be transported away from Ireland "most of the time".
The department also said it monitors the UK nuclear sector on an on-going basis and has regular talks with UK counterparts on general radiological policy and to raise matters concerns.
An Taisce, Ireland's national trust - which unsuccessfully challenged the British government in the courts in London over plans for Hinkley - said their fight was totally different than the Commission's inquiry and had been on a specific environmental issue.
Michael Colreavy, Sinn Fein energy spokesperson, branded Hinkley a regressive step.
"Energy policy under the Tory government has been at odds with public concerns about the environment and people's health. This is demonstrated by the British government's fervent promotion of fracking," he said.
"There will be obvious concerns from Irish citizens about the construction of a nuclear power plant so close to Irish soil."