British Energy is to invest £4.5m to meet safety standards at the Hunterston nuclear power station in Ayrshire, raising hopes that its life will be prolonged when the company reviews the issue next April.

The shares rose 28p to 548p as the utility yesterday published the findings of the Nuclear Installations Inspectorate's (NII) Periodic Safety Review (PSR) ahead of the scheduled reopening later this month of the two reactors at Hunterston B, along with two at Hinkley Point B in Somerset. All four reactors have been shut since last autumn because of boiler tube safety concerns.

"NII has concluded that the issues arising from its PSR assessment are not immediate concerns for nuclear safety," the inspectorate says in a letter to the company, "and that it is appropriate that normal station operation should continue whilst a remedial programme of work is progressed".

It goes on to warn, however, that health and safety improvements "cannot be deferred for reasons of affordability, so safety-related work does need to be resourced adequately, notwithstanding its effect on company finances".

While commending much of the safety monitoring work done internally by British Energy, the inspectorate says the company's submission to the review had "a number of significant shortfalls both in the quality and scope of information that is required by the UK regulatory system". It mentions that "a specific fire scenario (details withheld) should be investigated with due urgency".

British Energy says it will meet the requirements of the review with an ongoing £4.5m investment programme.

The NII concludes: "It is a challenging programme of work, and we have accepted your assurance that it can be carried out without adverse effects on other safety-related work.

"We have decided that formal enforcement action is not warranted at present, but that your performance in discharging the work programme will be closely monitored, and any slippage will be reviewed against our options for further enforcement actions."

It says that, if satisfactorily completed, no further safety review should be needed before January 2017.

British Energy said: "The company continues its work on assessing the accounting lives of Hunterston B and Hinkley Point B and expects to make a decision by March 2008 on economic and technical grounds as to whether the stations can be extended beyond their existing accounting lives of 2011."