Plans for the world’s biggest offshore wind farm have been hampered by fears that the noise of construction will disturb porpoises.

A decision on planning permission for Dong Energy’s 1.8 gigawatt Hornsea Two project, which would see up to 300 turbines built 55 miles off the coast of Yorkshire, had been expected in June.

However, it has been delayed until 16 August after the Department for Environment, Food and Rural Affairs proposed designating a 14,000sq m tranche of the North Sea – including the 186sq m area of the proposed wind farm – as a Special Area of Conservation (SAC) for the harbour porpoise.

In a statement, Minister of State for Energy and Climate Change Andrea Leadsom said: ‘This extension is to enable the Secretary of State to obtain further information in order to fully assess the possible impact of the Development on the Southern North Sea possible Special Area of Conservation for harbour porpoise, and to ensure that her duties in relation to the requirements under regulation 61 of the Conservation of Habitats and Species Regulations 2010 have been met.’

A Habitats Regulations Assessment must be carried out to look at ‘the likely significant effects of the project’ on the porpoise protection zone.

Ministers will take the final decisions on whether to proceed with the proposed SACs based solely on the scientific case presented following the initial selection process and consultation responses.