The estimated power of the fireball was equivalent to 4.3 million watts of energy.

The heat was so intense that part of the electrical breaker’s metal tool was vaporised and a 500 amp fuse was blown in a nearby electrical substation.

The Health and Safety Executive prosecuted Birmingham firm RVB Investments UK Ltd and manager Clifford Leigh following the incident on 10 August 2010.

Telford Magistrates’ Court heard RVB Investments’ employees Eamonn Osborne, 53, and David Rawlins, 46, had been told to find an underground water leak at an empty industrial unit owned by the company at Halesfield 5, Telford.

Leigh instructed them to dig at a spot outside the unit. Using an electrical drill, they drilled nearly 40cm into the ground until they hit a live 1,000 volt cable.

They were engulfed in a fireball and suffered burns to their hands, arms and faces.

Both were airlifted to hospital and Osborne was so seriously injured that for the first few days, doctors believed he might not survive.

RVB Investments had not assessed the risks involved, devised a safe system of work or obtained site plans of the area, checked whether there were any electrical cables underground or used safe digging methods.

The two men had also received no training about the dangers arising from underground services.

RVB Investments pleaded guilty to safety breaches and was fined £10,000 and ordered to pay £4,420 costs.

Clifford Leigh, of Birmingham, also pleaded and was fined £2,000 and ordered to pay £1,000 costs.

Speaking after the hearing, HSE principal inspector Nic Rigby said: “Companies must take measures to protect workers who are digging into the ground, where gas and electricity services may be found.”