British Energy yesterday signalled the controversial resumption of nuclear power plant construction in the UK, while admitting that continuing maintenance problems with two of its oldest plants including Hunterston in Ayrshire might threaten their future.

Any new construction would be on "one or more" of its existing sites, British Energy said.

The company extended to April the expected closure of the two Hunterston B reactors, which along with two at Hinkley Point B in Somerset have been closed for repairs to cracked boiler pipes since last autumn. Both plants had been expected back on line next month.

Bill Coley, chief executive, said the company would decide within 14 months whether or not to prolong the life of the two stations.

"The boiler issues are one factor in the life extension decision and always were a factor," Coley said.

"We are certainly interested in pursuing it, if it made economic sense depending on projected operating capacity and forecasts of electricity prices, along with all other factors."

Angelos Anastasiou, an analyst at Evolution Securities, said: "The ongoing boiler problems continue to be disappointing, especially the potential lack of life extensions."

Coley said the pipe repairs at Hinkley were complete, while at Hunterston they would be completed by mid-March, but other work already planned for April would now be brought forward to avoid a "double outage".

The rescheduled work in Ayrshire is on reserve feed water tanks, a spokeswoman for the firm said, and would take "a number of weeks".

British Energy has asked the UK's nuclear safety watchdog for permission to run both plants at only 70% capacity when they do restart. It is still looking into when the units can safely return to full output.

Coley said the boiler problems meant British Energy's plant investment over the next financial year would be at the top end of its £250m-£300m range of planned spending.

Meanwhile, the company said it was looking for partners to work on new nuclear generation projects in the UK. The group, which operates eight nuclear stations capable of providing one-fifth of the UK's energy needs, said it would look to develop capacity on one or more of its existing sites, which include Torness in East Lothian.

The moves come ahead of next month's publication of the government's white paper on energy, which is expected to pave the way for the continued role of nuclear power in UK supplies.

Coley said: "We have today launched a process to invite potential partners for new nuclear generation projects in the UK. Construction of new nuclear power stations is critical to meeting the UK's security of supply and climate change objectives."

He said it was an "exciting opportunity" for the company, which was the subject of a government-backed financial rescue in early 2005.

French group EDF and German group RWE are likely to be among the potential partners.

The shutdowns at Hinkley Point B and Hunterston accounted for the majority of the 9.6% drop in electricity output over the nine-month period to 44 terawatt-hours.

However, the drop in output was offset by higher power prices and consequently the utility, said nine-month earnings had shot from £462m last year to £775m, above analysts' forecasts of £748m.

British Energy shares fell 14p to 410p.