Oil giant Shell has been accused of operating platforms in the North Sea at dangerously high risk levels.
Former senior manager Bill Campbell, who led a safety review, claimed the company ignored his warning in 1999 that an accident was bound to happen.
Four years later two men were killed by a gas leak on the Brent Bravo platform.
Shell dismissed the claims. It said: "The allegation regarding operating with high risk levels is untrue and we absolutely refute this."
The company added that it had responded to the review and put a detailed improvement plan in place.
Keith Moncrieff, 45, of Invergowrie near Dundee, and Sean McCue, 22, of Kennoway in Fife, died after being overcome by a massive release of hydrocarbon gas in September 2003.
Shell was later fined ú900,000 after admitting health and safety breaches, including failing to carry out a risk assessment on the platform.
Speaking to BBC's Frontline Scotland programme, Mr Campbell said during the safety management review in 1999 he had been particularly shocked at what he discovered on Brent Bravo.
He said he found equipment was being operated in a dangerous condition, vital maintenance was being ignored and that lies were being told to cover it up.
It was also alleged that some emergency shutdown valves on Brent Bravo were not closing and platform managers reported 96% compliance with safety critical maintenance while the actual levels of compliance were 14%.
Mr Campbell said: "If you operate offshore installations at dangerously high levels of risk, the implication of that is that a major accident event will happen.
"It is a surprise to me that it took as long as 2003 before that happened."
Colin MacFarlane, professor of subsea engineering at Strathclyde University in Glasgow, said the Brent Bravo accident could have been a large-scale disaster because of the safety flaws identified by Mr Campbell.
"Bill Campbell identified things and made it plain to the management and Shell at that time that these things were wrong and dangerous," he said.
"If Shell, in 1999, had listened to what he said and taken action then, then the two guys wouldn't have died."
In a statement, Shell said it launched an independent internal investigation last year following concerns expressed by Mr Campbell.
It said: "This recent investigation, which we took very seriously, showed that there had been a vigorous and significant management response to the safety review, including a detailed improvement plan with action being taken, and progress reviewed by senior management."
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