Four Suffolk men were killed after an underground cage they were working in collapsed “like a picnic table”, an inquest heard.

The tragedy unfolded at Claxton Engineering, in North River Road, Great Yarmouth, where a high pressure test bay for offshore components was being built.

Daniel Hazelton, 30, and Adam Taylor, 28, both of Rickinghall, and Thomas Hazelton, 26, and Peter Johnson, 42, both of Stanton, near Bury St Edmunds, died on January 21, 2011.

The men had been working inside a cage below ground level in an excavation the length of a tennis court, the 11-strong jury heard.

The steel structure was to reinforce the concrete base of a unit to test offshore pipes, forming part of a £1.5million new test facility.

John Elvin, for the HSE, described the moment that the cage collapsed with the men inside as a “racking movement” best likened to a “collapsing picnic table”.

While the men were killed more than three years ago, Norfolk’s coroner has yet to record a cause of death following a lengthy police investigation which ruled out manslaughter charges.

Operation Madera, headed jointly by Norfolk police and the Health and Safety Executive (HSE) ran for 13 months and the file was with the Crown Prosecution Service (CPS) in London for around a year.

But in February 2013 the CPS ruled that no criminal charges – of individual gross negligence or of corporate manslaughter – would be brought.

Detective Chief Inspector Andy Guy, of the joint Norfolk and Suffolk Major Investigations Team, said he had challenged this decision but the result came back the same.

Speaking on the first day of a week-long jury inquest at Sprowston Manor yesterday, Det Ch Insp Guy expressed concern that the case had been passed between lawyers three times.

“I just wanted a separate opinion as after a 13-month investigation I understood things a certain way,” he said. “I just wanted to make sure everything was clearly understood.”

But he conceded that the CPS must have deemed there to be no realistic prospect of securing a conviction.

The HSE has yet to reveal whether a civil case will be pursued.

In a presentation, John Elvin of the HSE said the men were working on the reinforced concrete base of a horizontal test bed when they died.

He said access to the trench was via a ladder, some of the side wall had collapsed and water needed to be pumped out of it.

The area was “marsh land” and had needed piling work earlier in the build, he added.

The site was deemed unsafe for investigation after the deaths due to unsupported side walls, and further piling work was needed.

Mark Aylen, procurement manager for Claxton Engineering, said he had raised concerns about the men working inside the metal cage.

He said he had seen Thomas “squeezing” through and had been concerned it would take him a long time to get out if there was an emergency.

But he said a worker for project builders Encompass had assured him groundwork sub-contractors Hazegood knew how to work properly.

Mr Aylen added: “He jokingly shouted down, ‘I bet you’re glad you went on that diet now Tom’ and he smiled at me.”

He also expressed concern that the edges of the trench were crumbling and that he said staff did not always wear protective eyewear or hard hats.

But he added: “I never thought it was going to collapse.”

Robert Horner, for the families of the deceased men, questioned Mr Aylen’s role in health and safety.

Mr Aylen admitted there had been “no formal handover” when the previous Claxton project manager left for Dubai in October 2010, he had left risk assessment matters to Encompass and did not know Hazegood had been employed as sub-contractors until the day work began.

Scott Wilson Group had designed the test facility, the inquest was told.

Senior coroner Jacqueline Lake is set to hear further evidence today as the inquest continues.