Who is responsible for health and safety when work is contracted?

Three companies in Dundee have been fined for breaches of health and safety regulations following a fall that caused one worker multiple injuries.
The electrician’s labourer had been employed by one company that had been contracted by another to carry out works for a third company. On the day in question, the young man of twenty-three was working at height when he fell through a roof light to the ground below, striking machinery on his way down.
His left shoulder was dislocated and fractured and required three tendons to be reattached in surgery. He also suffered from multiple fractures to his back and puncture wounds from a drill bit he was carrying in his pocket.
Such serious injuries have compromised his future and his mobility, and he still suffers from chronic pain more than three years after the accident.
Following an investigation, all three companies involves were prosecuted for a range of reasons. None of the companies had conducted a job-specific risk assessment, despite the need to work at height. Health and safety training, inductions and supervision were not provided.
As a result, the three companies were fined a total of £336,000.