The UK Government has deferred its decision on whether to grant planning permission for Wylfa Newydd.
Developers Hitachi are seeking a Development Consent Order for the £12 billion nuclear power plant, despite putting its plans on hold.
The Business Secretary was expected to give the go ahead, but on Wednesday, Andrea Leadsom said she wants more evidence on the potential impact of the project, including environmental concerns.
A final decision is now expected by the end of March next year.
Horizon Nuclear Power, a division of Hitachi, said it was disappointed by the announcement, but would consider Ms Leadsom’s comments in detail.
The Department for Business, Energy and Industrial Strategy has now given a deadline of the end of the year for Horizon and other key bodies to submit further evidence, including Natural Resources Wales, Anglesey Council and the Office for Nuclear Regulation.
A spokesperson said: ”There are outstanding issues which mean that we are unable to reach a decision based on the information provided to us.”
”The Secretary of State has therefore extended the deadline for deciding the application to allow further information in respect of environmental effects and other outstanding issues to be provided and considered.”
”The applicant and other interested parties will be given until 31 December 2019 to respond to our request for further information. This will then be assessed, potentially including public consultation, and a final decision taken on or before 31 March 2020.”
Hitachi suspended all work on Wylfa Newydd in January, after talks with the UK and Japanese governments broke down.
Last week, energy giant EDF told an engineering magazine it would not its own bid for the site, but said it remained the ‘best site’ in the UK for a new nuclear build.
Before the announcement, opponents against the project called on the Business Secretary to reject Horizon’s planning application and concentrate on renewable energy.