Hartlepool Power Station, and its sister plant Heysham 1, in Lancashire, were due to re-open some time between the second and third quarter of this year.

The two nuclear power stations have been out of action since last autumn after wire corrosion issues were identified within boiler units.

British Energy chairman Sir Adrian Montague told shareholders yesterday there had been some delays, and that the sites may not return until the third quarter of the financial year. That covers the three months to the end of December.

The company also said the cost of the project will be "significantly higher" than initial estimates of £50m for the current financial year.

The Mail revealed last month how energy chiefs were spending £35m in a power station investment package while the plant was out of action.

It included £25m to modernise the inside of the plant, an £8m project to replace a mile of underground pipes and more than £2m on a new skills training centre.