The timeline for EDF to decide whether to go ahead with the £20bn Sizewell C power station has slipped amid a lengthy planning approval process that is playing out as funding negotiations with ministers continue.

The French power giant now expects to make a final investment decision on the Suffolk plant at the end of 2022 or in 2023, compared to its previous expectations of mid-2022.

The plant, set to generate enough power for about 6m homes, would be the second new UK nuclear plant in a generation after Hinkley Point C in Somerset, which EDF is building with minority Chinese partner China General Nuclear (CGN).

Almost all of the UK’s ageing plants are set to shut down by the end of this decade, leaving a gap in the nation’s power supply just as demand grows due to rising use of electric cars.

Nuclear power provides about 17pc of the nation’s annual power supply, and maintaining at least some of that capacity is regarded as important in Whitehall because it does not generate carbon emissions.

EDF is in negotiations with the Government about a funding deal for Sizewell C and will also need external investors.

Legislation is likely to be brought forward to allow developers to recoup costs during construction from household energy bills.

However, talks have been overshadowed in recent weeks by reports that ministers are seeking ways to block CGN from Sizewell and future UK nuclear projects. CGN has a 20pc development stake in Sizewell with an option to participate in the construction phase.

EDF submitted its application for a development consent order to the planning inspectorate last May, delayed by two months due to the pandemic, and has since made more than a dozen changes.

It has just submitted plans to build a temporary desalination facility alongside the site to provide fresh water to the plant during construction, involving up to nine 40ft shipping containers.

Northumbrian Water, which owns local water supplier Essex & Suffolk Water, has said a new mains pipeline will be needed to bring in water from another catchment area, but is unlikely to be ready until at least 2026.

An EDF spokesman said it wanted the planning approval process to be as thorough as possible so that local communities’ and others’ feedback is listened to and the best design for the plant is developed.

Stop Sizewell C, a local campaign group, said the changes to the water supply plan “exemplifies just how wrong this project is for our area, lacking the necessary infrastructure”.

Both Sizewell C and Hinkley Point C will use the new European Pressurised Water Reactor technology which has been deployed for the first time at a plant in Taishan majority-owned by CGN, with EDF holding 30pc.

The plant, which has been running since late 2018, was shut at the end of last month for “maintenance” due to cracked fuel rods, with small levels of radiation detected in cooling waters around the rods.

Sizewell C is expected to take between nine and 12 years to build.