Father-of-three Gary Walters, 51, was working for Gloucester-based contract haulier Larkins Logistics Ltd when the fatal incident occurred on 11 October 2010.
He was collecting a trailer loaded with structural concrete products from Bison Manufacturing in Swadlincote, Derbyshire.
He failed to apply the brake in his cab and, because Bison’s drivers had not applied the brake to the trailer, the vehicle moved off as he was coupling the two parts together.
Walters is believed to have gone round the front of the vehicle, possibly in an attempt to get into the cab and apply the brakes, but he was struck by the cab and run over. He died of multiple injuries.
An HSE investigation found that drivers working for Bison did not routinely apply the trailer brakes to ensure the units were safely parked.
Following the tragedy, a police vehicle examiner examined ten other trailers at the site but none had the brakes applied, and no other manual system of restraint, such as chocks or hooks, was in place.
Derby Crown Court heard that there had been a number of other instances of lorries rolling away and Larkins’ drivers had not been properly trained to assess the use of trailer brakes in the yard.
Both companies had identified the risk to workers, but had failed to implement appropriate control measures.
Larkins Logistics Ltd of Staunton, Gloucester, was found guilty of safety breaches and fined £450,000 and ordered to pay full costs of £23,317.
Bison Manufacturing of Dartford, Kent admitted the same charges and was fined £300,000 and ordered to pay full costs of £21,341.
After the hearing HSE inspector Judith McNulty-Green said: “This was not an isolated incident – sadly there are deaths and serious injuries to drivers every year in similar circumstances. It happened out of poor practice and was entirely preventable.
“Bison Manufacturing Ltd failed to implement a safe system of work for the storage of trailers with the brakes applied.
“They and Larkins Logistics Ltd also failed to implement and monitor working procedures for coupling and uncoupling trailers in the yard, and they failed to do it despite previous incidents.
Walters had three children with his wife Vanessa – James, who was 19 at the time of the incident, Joanna, 15, and Tanya, 13.
Mrs Walters said: “I hope that people learn from this tragedy and that today’s prosecution will go some way to changing the way people in the same industry work. I do not want this to happen to another family.
“Telling our children their dad had died was the worst experience of my life. I felt so helpless that they were hurting and that there was nothing I could do to make it better. As a parent you want to protect your children at whatever cost.
“James is 21 now and starting his own family. It’s sad that Gary never got to see his first grandchild.
“When the girls get married it won’t be a traditional wedding as their dad won’t be there to give them away. Gary will be missing from all the family portraits. There will never be a full picture again.”