The UK government has delayed a consent decision on Vattenfall’s planed 340MW Thanet Extension offshore wind project off southern England, asking for more details over a clutch of outstanding issues from seabed leasing to fish impacts before saying yes or no.

Energy secretary Andrea Leadsom was due to reach a decision on Thanet Extension on 11 December, but that has been put back to a date yet to be fixed for the Swedish developer and others to provide more input.

Thanet Extension, which would add to the existing 300MW Thanet project off Kent, is the furthest advanced in planning of almost 3GW of extension projects planned for the UK’s offshore wind fleet.

In a letter announcing the delay, Gareth Leigh, head of energy infrastructure planning at the UK’s Department for Business, Energy and Industrial Strategy (BEIS), asks for more details on a range of issues.

They include whether a leasing agreement has been reached with UK seabed landlord The Crown Estate, and the maximum generating capacity allowed.

BEIS also invited comments from interested parties over changes submitted by Vattenfall late in the examination process to the draft development consent order.

The government officials want an update on previously unresolved negotiations between the developer and UK conservation charity the National Trust over land acquisition, and with the nation’s Marine Management Organisation over potential impact on herring and sole spawning areas. The letter indicates the government is considering restrictions on percussive piling between November and May to address the latter.

The various parties have until 13 December to make their submissions.

The delay comes soon after the UK government deferred a decision on consent for the world’s largest planned offshore wind project – Orsted’s 2.4GW Hornsea 3 – after bird charities raised last minute fears over its impact.

Thanet Extension has been an ambition of Vattenfall’s back as far back as the last decade, with plans dropped in 2010 but then picked up again in 2016. The developer has envisaged using turbines between 8-10MW at the site.

The Crown Estate in August said 2.85GW of projects, including Thanet, had been cleared to proceed down the planning process after a Habitats Regulations Assessment.

Vattenfall said in a statement sent to Recharge: “Vattenfall recognises the importance of seeking clarification and some final detail to ensure that the relevant information has been considered fully and that stakeholders have been properly consulted as part of the Development Consent Order process.

“We will cooperate with the Department for Business, Energy & Industrial Strategy to provide the requested information and updates.”

Note: Update adds Vattenfall comment.