On behalf of 21,000 members working in electricity generation, distribution and transmission, Prospect deputy general secretary Garry Graham said: “Today’s warnings from National Grid will not be news to our members working in the energy sector.

“Prospect has consistently warned of the dangers of declining generating capacity and reduced energy margins.

“It is simply extraordinary that energy intensive users will be incentivised to cease work at times of peak demand while consumers still face concerns about security of supply. What message does that send to investors?”

Graham added that recent isolated commercial decisions to close ageing plant had aggravated an already challenging position.

“It is imperative we invest in baseload generation now to keep the lights on long term, implement a balanced energy policy and provide consumers and businesses with the security of supply they deserve.”