Scottish and Southern Energy has announced it pulled out of the NuGen UK nuclear new build consortium.
The British utility said it had decided to focus on renewable energy and gas-fired power plants, which are technologies it has more experience with.
"We have concluded that, for the time being, our resources are better deployed on business activities and technologies where we have the greatest knowledge and experience," said Alistair Phillips-Davies, SSE generation and supply director.
Its partners GDF Suez and Iberdrola have raised their stakes in the nuclear consortium to 50 per cent each, reiterating their commitment to the 3.6 gigawatt new build project at Sellafield in West Cumbria.
The NuGen consortium plans to starts its first new station around 2023.
"We are highly confident about our prospects in respect of our development plans in West Cumbria and there is no reason why this decision by SSE should impact upon our plans or timetable," Iberdrola and GDF Suez said in a joint statement.
SSE said it may get involved again in the project in future as an investor or to buy power from the nuclear plant, but in the meantime renewable energy and gas-fired power plants including carbon capture and storage were its priorities.
The announcement comes just two months after the British government announced ambitious plans to reform the electricity market to reduce carbon emissions, delivering a blow to the UK's nuclear new build programme.