German utilities E.ON
The companies want to withdraw from that, said a source close to the companies and informed about the developments.
Both companies and their joint venture Horizon declined to comment.
They had planned up to 6,000 megawatts of new nuclear plants in Britain by 2025 due to national legislation that was more friendly towards nuclear energy than in other countries as the UK seeks to lessen carbon emissions.
But the companies had been indicating recently that they were concerned about possible cost overruns as seen at other nuclear projects in Europe.
(Reporting by Tom Kaeckenhoff and Karolin Schaps, writing by Vera Eckert)