National Grid has brought forward plans to tap additional power capacity over the winter after unexpected plant outages.
It is being described as a precautionary move, supported by Government, to safeguard supply rather than any bid to prevent possible blackout.
National Grid said it had launched a tender for its Supplemental Balancing Reserve (SBR), asking power firms how much more electricity they could provide the network to fill a potential gap from mothballed or closed generators.
The network operator cited a series of unplanned shutdowns at large power stations for its decision to begin SBR a year ahead of its original timetable, having previously warned of a looming supply crunch.
Fires at E.ON’s Ironbridge and SSE’s Ferrybridge power plants have reduced output while precautionary checks at EDF Energy’s Heysham and Hartlepool nuclear plants have also hit production.
The worries over future supplies were initially sparked by ageing and most-polluting power stations being shut down at a time when new plants are struggling to make up the shortfall.
National Grid’s plan to safeguard supplies at peak winter times also includes a scheme that allows it to ask contracted users, mostly factories, to reduce their electricity demand when the system is strained.