Bola Akinola, 48, fell more than four metres when steelwork supporting concrete floor planks failed causing the collapse at a site in Westerham, Kent on 9 May 2009.

Akinola, of Littlehampton, West Sussex, suffered multiple fractures to his pelvis, leg and arm.

He was in hospital for several weeks and was unable to work for nearly a year. He has still not regained full mobility in his left arm.

Esher-based Landmark Groundworks Ltd was prosecuted during a nine-day trial at Maidstone Crown Court

The court heard Akinola was helping to build a large new basement alongside an empty house that was being refurbished and extended. Landmark Groundworks was contracted to oversee the project and provide supporting steelwork.

On the day of the incident, a separate subcontractor who employed Akinola,  had laid around 50 concrete floor planks, each weighing up to two tonnes, for the ground floor.

Four planks were laid on a beam that had not been fixed at one end and only held with small welds at the other. As a result the beam tilted and gave way while workers were still on the planks.

Akinola, a plank installer, fell four metres into the basement with the collapsing steel and three of the floor planks. Another worker managed to jump to safety as the floor gave way.

An HSE investigation found that Landmark Groundworks  had ignored design proposals by two structural engineers that would have helped ensure the project was carried out safely.

In addition Landmark did not carry out checks on the installation to ensure it was ready to load out.

The company, of Wren House, Portsmouth Road, Esher, was fined £110,000 and ordered to pay £50,000 in costs after being found guilty of safety breaches.

After the hearing HSE Inspector John Underwood said: “Buildings do not build themselves. The process needs to be actively managed to ensure that subcontractors get the correct information and use it.

“It is completely unacceptable for a main contactor, Landmark Groundworks Ltd, to allow work to continue with a botched design, and with no checks carried out on either the design or the installation.

“This incident resulted in life-changing injuries to Mr Akinola and it was a matter of luck that the collapse of nearly nine tonnes of building material did not result in multiple fatalities.”