On a high turnout of an 80% of Prospect’s members in the company’s distribution network, nearly 99% voted for action short of a strike. The action, expected to start on October 24, will see Prospect members in EDF Energy refuse to work beyond their contracted hours and a general withdrawal of goodwill and cooperation.

While members are adamant that safety will be paramount, the action will, for example, mean that staff working on standby arrangements will ensure any problem sites are safe but will not begin remedial work until normal working hours resume.

Prospect negotiator Azim Hajee said: "EDF management’s refusal to improve on a pay offer which effectively imposes a pay cut on staff is doubly insulting, coming at the time when the parent company EDF Group is boasting that business has never been so good.

"In the run-up to the launch of the anticipated share flotation, EDF Group is showcasing a general increase in sales and profits of 10%, while EDF Energy in the UK is celebrating an increase in gross profits of 16%."

But at the same time the company is blaming the regulator for its inability to increase a pay offer of 2.3% which was 0.9% below inflation in April and is now over six months late.

"On one hand the company acknowledges that these record profit levels would be impossible without the support of staff. But on the other, it expects the same staff to pay the price of penalties imposed by the regulator due to efficient operational management. No wonder staff feel forced into taking action."

Given earlier warnings from the Met Office and the electricity industry that a predicted cold spell could present real challenges in keeping the lights on this winter, Hajee warned: "EDF Energy may regret this cavalier attitude towards its staff."

Prospect represents staff working in professional and engineering grades in EDF Energy. Industrial action is rare in the electricity supply industry with any previous precedents for formal industrial action by professional and engineering grades dating back to the mid-70s.

As one of the largest regulated and private network operators, EDF Energy distributes electricity to over a quarter of the UK population, including 7.8m homes and businesses across London, the east and south east of England. It has important contracts with BAA’s Heathrow, Gatwick and Stansted airports, the Channel Tunnel Rail Link, the London Underground and Canary Wharf.