British Energy shares dipped sharply yesterday after the nuclear generator confirmed yet another repair problem affecting one of its ageing reactors.

The company said inspections of Heysham 1 Reactor 2 had "so far not shown any evidence of broken wires" in the boiler closure unit.

"However, there is evidence from the radiographic inspections that are in progress that one wire is showing signs of thinning. This will likely place the Reactor in the same category as Hartlepool Reactor 1 and Heysham 1 Reactor 1 for a return to service safety case and/or remedial repairs."

The problem first emerged during a statutory inspection of the Hartlepool reactor, which had been scheduled to restart this month, when it was discovered that a wire had failed owing to corrosion.

The company warned a month ago that it was taking the "conservative decision" to inspect the wiring at all the reactor's sister units, three in all, at Hartlepool and Heysham, and earlier this month said a similar problem had been found at the first Heysham reactor.

The design of the boiler closure units is unique to the two nuclear stations, and the problem is described as a "legacy issue of the initial construction".

The shares gave up 19p to 458.75p.