The UK's Health and Safety Executive (HSE) has identified flaws in the design of nuclear plants, it has been revealed.
The French and American-designed nuclear reactors are part of ambitious plans to reduce Britain's dependence on coal-fired power stations.
But in the first part of a safety assessment, the HSE has found a "significant number of issues", adding that the process cannot move forward until these are fixed.
Earlier this month, Energy and Climate Change Secretary Ed Miliband announced plans to build ten nuclear power stations, the first of which is meant to be up and running by 2018.
But before construction can begin, the safety issues with the plants have to be resolved as part of the HSE's general design assessment, it said in its report.
"If these are not progressed satisfactorily then we would not issue a design acceptance confirmation," the agency said in its report – which marks the end of the third stage in a four-part approval process.