The 48 year-old casual labourer fell three metres to the ground at the site in Ruskin Road, Tottenham, on 14 September 2012, with the concrete blocks falling around him.

He sustained serious breaks in the lower leg bones and needed a major operation and a skin graft. He still cannot walk properly and is unable to return to work.

A colleague at ground level narrowly escaped being hit.

Westminster Magistrates’ Court heard that instead of laying three courses of blocks onto joist hangers, the first floor had been loaded with two piles, each of 88 concrete blocks weighing 1.6 tonnes.

The labourer was piling up the blocks on the first floor and without the vital strengthening block work, the collapse was inevitable.

Cosmos Builders 88 was aware of the correct construction method, as eight previous houses on site had been properly completed, but had gone ahead regardless to ‘keep the workers busy’.

HSE inspectors also found poor management had led to builders had been put in unnecessary danger by being told to work at height in areas where there were no safety measures in place.

When questioned at the time, the company said they wanted to keep the workers busy while awaiting for scaffolders to arrive.

Cosmos Builders 88 Ltd, of Leyton, Waltham Forest, London, was fined a total of £6,000 and ordered to pay £4,000 in costs after pleading guilty to safety breaches

After the hearing, HSE Inspector Keith Levart said: “Both offences were caused because the Cosmos Builders instructed workers to undertake tasks that they knew to be unsafe, but were unwilling to halt the work.

“In terms of the collapse, the firm cut corners by not carrying out the first floor work to the accepted standard and then allowed it to become grossly overloaded.

“As a result, a casual labourer has suffered an injury that may prevent him from returning to manual employment for a considerable time.

“Cosmos Builders 88 Ltd did not pay enough attention to the tasks being undertaken and failed to fully appreciate the risks involved.

“For this reason, it is hugely important that if something alters on site, such as materials being late, managers must take the responsibility to re-assess the risks and make sure there are no unintended – and possibly fatal – consequences.”