The incident occurred on 13 September 2006 at the company's Wigton, Cumbria facility.

Gordon Metcalf, 62, and another employee who did not wish to be named, were about to clean debris from a damaged fuse box when a ball of fire shot out, setting both men's clothes alight.

Cumbria Crown Court was told that here had been a fire in the fuse box the previous day, but live cables had been routed through it so the cooling equipment at the factory could continue to operate, thus avoiding a 36-hour shutdown of the plant.

Mark Dawson, HSE principal inspector for Cumbria, said: "Two workers have suffered devastating injuries that will impact on them for the rest of their lives.

"It was an astonishing decision to allow work to go ahead without the live electricity supply being switched off, and even went against the company’s own work procedures. If the factory had been shut down for just a day and a half then neither of the workers would have suffered severe burns."

Metcalf suffered burns to 47% of his body in the explosion. He was in a coma for four weeks, intensive care for six weeks and in hospital for five months. Doctors did not expect him to survive, the HSE said.

"When I came out of hospital, I had to wear a suit over my head and body for a year and could only take it off to wash. I still have to apply cream three times a day to stop the scarring getting any worse.

"There’s no way I can return to return to work as an electrician as I struggle to grip with my hands. I’m also constantly short of breath and my skin flakes off if I knock my hand. I just wish Innovia had cut the electricity supply before asking us to do the work."

A statement from Innovia chief executive David Beeby said: "Innovia Films and its employees have co-operated throughout with the HSE investigation, and the company entered a guilty plea to the charge.

"We are, of course, extremely sorry for the suffering caused to our two injured colleagues and are pleased that we were able to deal with this matter in a way that saved them from having to give evidence and relive the events of nearly five years ago.

"Innovia Films remains absolutely committed to health and safety. We have worked hard to further improve our safety system to ensure that such an accident does not occur again in the future and that work will continue."