The bereaved and survivors of the Grenfell disaster have called for an urgent ban on the use of combustible materials in buildings after they said evidence at the public inquiry had revealed “fraud”, “cover-up” and “incompetence” in the construction industry. Their lawyer told the inquiry chairman, Sir Martin Moore-Bick, on Monday that methods of checking safety of materials had been revealed as “positively dangerous” and that a key independent testing centre for construction products had been “complicit in manufacturers’ frauds”. “It may be that the only answer – in the short term at least, pending stricter product regulation and the necessary advances in competence … is to insist that non-combustible materials are used,” said Stephanie Barwise QC. Ministers have so far banned combustible materials only on high-rise blocks, and have yet to decide whether to widen the ban on combustible materials after launching a consultation 21 months ago. Leaseholders in hundreds of other high-rise blocks condemned as unsafe are preparing a mass protest at Westminster on Thursday to demand the government protects them from an estimated £15bn nationwide bill to fix post-Grenfell fire safety faults. A new building safety bill is passing through parliament but Labour and Conservative rebels warn it does not offer leaseholders sufficient protection from costs that in the worst cases exceed £200,000 per household. Barwise was speaking at the end of the inquiry’s investigation of the testing, certification and marketing of combustible materials that spread the 14 June 2017 fire and released toxic smoke that together killed 72 residents. She said the evidence showed that the process of giving safety certificates to construction products concealed results obtained through “dishonest testing”. The behaviour of some at the Building Research Establishment, which tests construction designs for safety, “amounted to complicity in manufacturers’ frauds”. One of its technicians, for example, knew that fire-retardant boards had been added to a test rig to improve fire performance ratings of the Celotex plastic foam insulation that was used on part of the building. “Frauds practised on the market by Kingspan, Celotex and Arconic were compounded by the ‘complacent’ test houses which ignored warnings about shortcomings three years before the disaster,” she said. Kingspan, Celotex and Arconic have all denied cheating the market. Arconic, which made the panels, has said it was the responsibility of others to ensure its products were used in line with building regulations and has said the certificate for its panels made clear it was the surface, rather than the whole panel, that had the highest rating for fire spread. Kingspan has said it never claimed its insulation would comply with building regulations if combined with ACM cladding. Celotex has said its material could have been used safely with non-combustible cladding panels, while BRE has said Grenfell’s cladding differed from systems it tested for Kingspan and Celotex and it should have been separately fire-tested. Barwise also said that the building control officer at the Royal Borough of Kensington and Chelsea who signed off the Grenfell works had “a woefully flimsy grasp of building regulations”. She said most construction professionals involved showed “lack of competence … seeming ignorance of their obligations and refusal to take professional responsibility for their actions”. The counsel for RBKC, James Maxwell-Scott QC, said: “The council apologises unreservedly for its failings.” RBKC admitted building control did not ask for the details of the cladding system, did not identify whether the materials were of limited combustibility or met building regulations guidance. The inquiry continues.