THE UK's largest structural steel firm has been fined £135,000 following the death of a forklift truck driver described by a judge as "perfectly horrific".

The parents of Kelvin McGibbon appeared emotional as Severfield, which employs 300 staff at its plant at Dalton Airfield Industrial Estate, near Thirsk, pleaded guilty to failing to ensure the safety of its workforce at Teesside Crown Court.

The sentencing hearing was told before Mr McGibbon, of Northallerton, was fatally crushed under the forklift truck he was driving in March 2013, an endemic culture of "not being bothered to wear a seatbelt", despite the high risks, had existed over numerous years at the plant.

Lisa Roberts QC, prosecuting for the Health and Safety Executive, said scores of employees, tasked with undertaking 30,000 forklift truck lifts annually at the £100m turnover firm, had been exposed to danger as it prepared steel for projects such as Heathrow Terminal 5, Cleveland Energy from Waste Plant, the Gateshead Millennium Bridge and the London Olympic Stadium.

The court heard employees, including the 27-year-old avid Manchester United fan had often driven the diesel-powered vehicles at high speeds, operated them while chatting on mobile phones and even leapt from them while they were still moving.

She said Mr McGibbon, who was not wearing a seatbelt and had been warned over driving forklifts too fast, inexplicably reversed at speed after delivering welding wire to a production line on the 78-acre site and clipped a raised concrete step.

His colleagues did not notice as his forklift overturned and he was thrown from the vehicle, before being crushed face-down, between the roll-cage and the ground, with a leg still in the truck.

She said moments later colleagues rushed to his aid and talked to Mr McGibbon, described in court as "popular, cheerful and upbeat", as emergency services were alerted. His family and staff were left devastated when he died soon after.

The court heard his death inspired a campaign for the Yorkshire Air Ambulance which had raised £9,000.

Ms Roberts said Mr McGibbon had received several rounds of training in which he was instructed to wear a seatbelt, but the rule was never enforced by Severfield.

She added: "It is incumbent on the employer to ensure risks remain at an acceptable level."

After Mr McGibbon's death the firm warned staff that failure to wear a seatbelt would result in instant dismissal.

The court heard Ian Cochrane, Severfield's chief operating officer, claim health and safety measures were at the core of what the firm did and highlight that it had been heralded for its safety practices while constructing the London Olympic Stadium.

John Cooper QC, mitigating, said while the firm had not caused Mr McGibbon's accident, Severfield had faced up to "uncomfortable truths" and had learnt lessons, enforcing rules on speeds, seatbelts and turning on slopes and introducing regular, rigorous and multi-layered safety checks.

He added: "It is quite rare in business to man-mark individuals. There has to be a degree of devolved risk to employees."

Judge Anthony Briggs said while Severfield had made clear efforts to ensure the safety of its staff, it had had a blind spot over the enforcement of wearing seat belts on forklift trucks.

He said he believed the fine, which he reduced from £300,000 after finding Severfield had taken steps to improve safety and had no previous convictions, would serve as a warning to other firms.

A spokesman for the firm declined to comment after the hearing.

It is understood while Severfield works on tight margins, the sentence will not affect its ability to continue employing all its staff.