Xian Hou Ye, 56, was crushed and suffocated by nearly nine tonnes of soil in the fatal incident at Waldram Park Road, Lewisham, on 30 September 2010.

Woolwich Crown Court heard that he was one of a group of workers contracted by Croxley Green-based HMB Services Ltd and company director Vijay Patel to convert an existing three-storey property into nine flats.

The property was co-owned by brothers Mukesh Shah and Kiran Shah, also from Hertfordshire, who appointed HMB Services and Patel as the principal contractor to oversee the project.

As part of the works, a large trench had been dug out that was approximately seven metres long, between one to two metres wide and almost three metres deep. This was being extended at one end at a 90-degree angle to form an L-shape.

A digger was helping to shape the extension whilst Ye was working in the deeper existing section.

As work progressed, the inside corner of the L-shape caved in and buried him under approximately 8.7 tonnes of earth.

He died at the scene despite frantic efforts to dig him out.

The Health and Safety Executive found the trench was inadequately supported with sheets of plywood and timber props.

More substantial supports or using a safer method of trench construction, known as battering, should have been used.

This was a failing on behalf of both HMB Services and Patel, who were responsible for the work, and clients Mukesh and Kiran Shah, who should have ensured their principal contractor was competent to carry out the project.

Mukesh Shah and Kiran Shah, both of Pindar Road, Hoddesdon, Herts, were each found guilty of two separate safety breaches.

Mukesh was fined £40,000 with costs of £34,750. Kiran was fined £25,000 and was also ordered to pay £34,750 in costs.

The brothers were told they would be jailed if they failed to make the necessary payments.

Vijay Patel, of Croxley Green, Herts, was ordered to undertake 270 hours of community work after pleading guilty to a single safety breach. The court ruled he had no means to pay a fine or contribute towards costs.

HMB Services Ltd, of the same address, is now dissolved so the company avoided prosecution.

After sentencing HSE Principal Inspector Russell Adfield said: “Mukesh and Kiran Shah were having this conversion undertaken as part of a business venture and they were therefore ‘clients’ in this project.

“A client has a very major influence over how a construction project is run as they have responsibility for appointing competent advisors – principal contractors – and ensuring that arrangements are in place for carrying out the project safely.

“The clients in this case failed on all fronts.

“They had no advisors to help them understand what was required of them, the principal contractor they appointed was not competent to manage this work safely and there were no formal arrangements in place to ensure the safety of those workers on site.

“It appeared neither the clients nor principal contractor had any understanding of the very real risks on that site – or how to ensure those risks were controlled.”