Dorchester Crown Court heard that James O’Connor was working on a cottage on a sloping site that needed excavating below the level of the shallow foundations to build an extension.

O’Connor was in the process of lowering the ground level when the gable wall collapsed knocking him to the ground.

At the same time, part of the wall fell through the windscreen of an excavator and activated the reverse lever.

O’Connor’s leg, which was on the track of the excavator, was pulled in and became trapped between the track and body of the excavator.

He suffered shoulder, back and leg injuries and had to have his right leg amputated above the knee.

The court heard that David Mitchell, a director of Ferndown Developments Ltd, had hired O’Connor to work at the cottage when the incident happened on 29 April 2009.

The HSE investigation found that Mitchell did not control the work in a safe manner. He failed to identify the need to support the building during the excavation and foundation stages of the project.

Mitchell, director of Ferndown Developments Ltd, of Wimborne, pleaded guilty to safety breaches and was fined £2,000 and ordered to pay costs of £18,000.

Speaking after the prosecution, HSE Inspector Frank Flannery said: “This was a very serious and wholly preventable incident in which a man in his prime lost a leg as a result of the omissions and failings during the planning and construction phases of the project.

“Had Mr Mitchell fully assessed the safety aspects of the work that he was contracted to do prior to starting, he would have identified the need to support the building during the excavation and the building of the new foundation.

“This would have allowed a structural engineer to be instructed prior to the work starting, and a safe system of work could have been determined.

“Whilst welcoming the verdict today, the fact remains that this incident could have easily resulted in a more serious outcome and is a reminder to all those in the construction industry of their legal duties to manage health and safety.”