Firms have been warned by the Health and Safety Executive (HSE) that they face fines and injury compensation claims if they fail to ensure their staff are fully trained to use vehicles.
The warning follows an incident in Berkshire in which a demolition labourer was injured while operating a skip-loading dumper.
While he was at work on a construction site the dumper overturned, trapping the employee beneath it and causing severe damage to his foot.
A HSE investigation found that the worker had received no formal training or instruction in operating the vehicle.
"Site dumpers are involved in around a third of construction transport incidents, causing many deaths and serious injuries, particularly to drivers," commented HSE inspector Karen Morris.
Recent HSE inspections at construction sites in West London resulted in 21 enforcement notices being served for unsafe working practices which put employees at serious risk of work injury.