Government has agreed a six-week delay to the final decision on the proposals for the Sizewell C nuclear power station.

But the Planning Inspectorate (PINS) has been told it must stick to the rules in future - because delays could erode developer confidence in national projects.

PINS has been handling the plans for the new £20billion nuclear power plant for the past 19 months, including a thorough examination stage.

But PINS says 22 changes made to the proposals by EDF during that time have created extra work and inspectors would not be able to meet the deadline by which they have to send their full report and recommendation to Government.

In addition to the changes during the process, and the size and scale of the project, the examining authority has also had some unexpected health issues that have caused a delay to report writing, creating "considerable pressure" for the small expert team.

In a letter to Kathryn Dunne, operations lead at PINS, Gareth Leigh, head of energy infrastructure planning at the Department of Business, Energy and Industrial Strategy, said secretary of state Kwasi Kwarteng had agreed to the six-week extension.

The final report and recommendation must now reach Government by February 25 instead of January 14.

Mr Leigh said: "While acknowledging the current difficult circumstances facing the Examining Authority at the Reporting stage of this project, the Secretary of State is keen that the Planning Inspectorate should ensure that future timetables, including the Reporting stage, are adhered to so that developer confidence in the certainty of timings under the Planning Act process for Nationally Significant Energy Infrastructure Projects is not eroded.

"He would be grateful, therefore, if you could reflect on the circumstances that led to this request for an extension in order to ensure as far as possible that they do not reoccur including how to build greater resilience into the Examining Authority process so that it is better able to cope with unexpected circumstances such as illness; and how to cater for situations that can be anticipated, such as very large volumes of documentation, strong and divided views, and some material changes for a nuclear project, all of which we have also seen in previous nuclear applications."

The scheme not only includes the twin reactor power station, but also a two-village bypass, link road, rail line upgrades and a temporary desalination plant.

A statement will be made to Parliament about the delay.