The man, who does not wish to be identified, fractured his right wrist and right eye socket and also suffered severe internal bruising in the incident at the White Horse Business Park on 14 January 2013.
He was unable to work normally for several months and still requires further surgery.
The fall occurred as he was undertaking cable installation work on behalf of an electrical contractor at Summit Chairs Ltd.
The company was prosecuted alongside sales director Roy Gurney after an investigation by the HSE found access for the work at height was inherently unsafe.
Swindon Magistrates’ Court heard that although a scissor lift was kept on site for such work, it was no longer available for use, and the equipment the workers were expected to use instead was entirely inappropriate.
HSE established that Gurney suggested raising a metal stillage or cage on the forks of a fork lift truck to provide a work platform.
He was aware that the stillage was simply resting on, but not secured to, the forks of the truck, with nothing to prevent it from sliding along the forks or tilting to either side.
The court was told that had the work been properly planned and managed, with suitable equipment in place, the incident could have been avoided.
Summit Chairs of Trowbridge, was fined £7,500 and ordered to pay £4,000 in costs after admitting safety breaches.
Gurney, of Broughton Gifford, Melksham, was fined £3,000 and ordered to pay £1,315 in costs for the same offence.
Speaking after the hearing, HSE Inspector Andy Shaw said: “Falling from four metres onto a hard surface often kills, and this incident could so easily have ended in tragedy.
“As it was, the worker was seriously injured because he was expected to work at a dangerous height using fundamentally unsafe means of access.
“Roy Gurney and Summit Chairs Ltd failed to properly assess the risk or plan the job accordingly.
“This case highlights the need for companies and individuals who engage contractors to ensure that working methods and equipment for work at height are safe and appropriate for the circumstances.
“The host employer is responsible for the safety of contractor’s staff as well as their own, and directors can be personally responsible for serious failings that result in significant injury or death in their workplace.”