Colin Riches, 54, of Ham Close, Ham, died from head injuries after he fell backwards following the 240 volt shock, an inquest heard last week.

He was taken to Kingston Hospital on September 13 and died eight days later from a brain haemorrhage.

Colleague Terence Byrne told St Pancras Coroners' Court that he was helping Mr Riches build a kitchen extension at a property in Richmond on the day of the accident.

He had been called in after another labourer dropped out of the job. The men spent the day fitting the kitchen worktops and at 3pm they started to pack the tools away.

Mr Byrnes said he suddenly heard a groaning noise and saw Mr Riches fall backwards with both his hands clutching the drill under his chin.

The court heard how Mr Byrnes unplugged the lead before wrenching the drill away from his colleague. He then tried resuscitating Mr Riches who appeared to have stopped breathing.

"I don't know if it worked but he actually sat up," he said.

When the ambulance arrived Mr Riches had recovered enough to argue with paramedics that he did not need to go to hospital.

The drill used by Mr Riches was described as having a metal casing. The court heard that the original wiring for the drill had been cut and different lead had been attached with some tape.

Health and safety inspectors were unable to examine the drill because Mr Byrne had thrown it on the site skip.

But Inspector Emma Davies, of the health and Safety Executive, told the coroner that the electric shock might have occurred if the drill's lead had not been properly attached.

She said: "If the casing had been plastic, there would still have been the potential for a shock if it was not wired up correctly."

Coroner Dr Stephen Chan recorded a verdict of accidental death.