The UN Court of Arbitration has begun hearing an Irish application to force Britain to disclose its financial plans and projects for the Sellafield nuclear plant.
Opening the Irish case, Attorney General Rory Brady said Ireland has a direct interest in information about the nuclear plant because of the effect that waste discharges have on the Irish Sea.
British Nuclear Fuels, which is owned by the British government, has refused to reveal information about its sales volume or estimates of future contracts, saying it is too economically sensitive.
However, Mr Brady argued today that that the figures could help indicate the levels of hazardous waste likely to enter or leave the plant, information that goes to the heart of international treaties governing radioactive pollution.
"The information affects Ireland's ability to assess the impact on the Irish Sea environment," he said.
"If there are substantial contracts, as the British government has argued there are, then that has consequences for Ireland."
Although this case is solely about the disclosure of information on the grounds of environmental protection, the Irish Government has confirmed that it is hoping to use any disclosed material in its campaign to have Sellafield shut down.
The British government is due to respond to Ireland's arguments tomorrow and the hearing is expected to last all week.
The three-judge Court of Arbitration has not set a date for when it will issue a ruling.