Completion of the Hinkley Point C nuclear plant has been delayed for up to another four years, according to the French company developing it.
The final cost of the power station, which will be the UK's first new nuclear plant in decades, could also end up being as much as £46bn.
The start of electricity production at the site had been scheduled for June 2027 - but a re-evaluation of the schedule suggests that one of the two planned reactors in Somerset will not be ready until 2029.
Another evaluation assumes it could be operational a year later, while a final scenario suggests adverse conditions could see that drag on until 2031, energy giant EDF, which is developing the plant, warned.
Meanwhile, the total bill for completing the project is now estimated at between £31-34bn in 2015 values - £46bn at today's prices. EDF has given cost estimates in 2015 prices for easy comparison over time.
The firm said if the risk of an additional 12-month delay on top of the three years - as imagined in the final scenario - did happen, it would result in an estimated additional cost of around £1bn in 2015 values.
EDF is aiming for the plant to become a major source of decarbonised electricity supply for the UK, providing around 7% of national consumption.
In a note to Hinkley project staff, Stuart Crooks, managing director of Hinkley Point C, said: "Like other infrastructure projects, we have found civil construction slower than we hoped and faced inflation, labour and material shortages - on top of COVID and Brexit disruption."
In December last year, building work on the multibillion-pound nuclear power station reached a major milestone, with the first reactor building being lifted into place.
EDF said the achievement ended the year on a high as the 14 metre-tall dome sat on top of the reactor building, which is 44 metres high.
It was said that around 10,000 workers and 3,500 British companies were involved in the building of Hinkley Point C.
The Somerset plant was originally supposed to have started producing electricity from 2017 at a cost of £18bn.