The 45 year-old worker, Paul Shaw, of Maidstone, suffered multiple fracture injuries, including a broken right arm, when he fell through the roof opening which had been covered only with a thick plastic.

The incident on 29 February 2012 took place at a property in Tonbridge, Kent, where Bryen & Langley Ltd was the lead contractor overseeing the construction of an extension and swimming pool.

Maidstone Magistrates heard that an HSE investigation found that Bryen & Langley Ltd had failed to ensure that proper safeguards were in place to prevent anyone falling when work was underway at height.

The court was told that skylight openings above the swimming pool had been covered with plywood sheeting.

This was changed to thick plastic to allow some natural light through and to enable workers to lower materials into the pool area if needed.

The plastic was then covered with pallets and held down by timbers.

Shaw, who was employed by a roofing sub-contractor on site, went up to the swimming pool roof and stepped on to a skylight opening believing it was safe to do so.

The hole was simply covered by the plastic and he fell straight through landing on the pool’s concrete walkway.

He now has restricted movement in his wrist but was able to return to work after five months.

Bryen & Langley, of Eltham, London, was fined £12,000 and ordered to pay £9,209 in costs by magistrates after admitting breaching safety Regulations.

After the hearing, Inspector Melvyn Stancliffe said: “The distance that Mr Shaw fell could easily have resulted in his death. He is a lucky man – though I am sure he did not feel so at the time.

“This incident was avoidable and Bryen & Langley, as lead contractor, had a responsibility for safety on the site. It would have been a simple matter to have fixed the skylight covers in place.

“If they then needed to be moved for any reason, then temporary protection should have been placed around the openings and a system employed to ensure coverings were replaced promptly and correctly.

“Work at height needs to be properly planned and there need to be sufficient measures taken to guard against people falling.”