A cladding company made "false and misleading claims" about its product being suitable for Grenfell Tower before the 2017 fire, an inquiry concluded.
The final report into the disaster has set out how a chain of failures led to the blaze that killed 72 people.
Cladding had already been found to be the "principal" reason for the fire's rapid spread.
Celotex, based in Hadleigh, Suffolk was one of two firms that made the insulation inside the cladding, but said decisions on Grenfell's selection of materials were made by "construction industry professionals".
In the final report by inquiry chairman Sir Martin Moore-Bick, firms including Celotex received heavy criticism.
The company "embarked on a dishonest scheme to mislead its customers and the wider market", Sir Martin concluded.
"One very significant reason why Grenfell Tower came to be clad in combustible materials was systematic dishonesty on the part of those who made and sold the rain-screen cladding panels and insulation products," he said.
Firms had "engaged in deliberate and sustained strategies to manipulate the testing processes, misrepresent test data and mislead the market", the report said.
A spokesperson for Celotex said it was considering the final report "with care".
They said the company conducted its own review immediately after the fire to "interrogate the circumstances in which the RS5000 product had been tested, launched and marketed".
"This review was a significant and thorough undertaking, and the...
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