The UK’s largest building control organisation was warned 18 months before the Grenfell Tower fire that “any number of buildings” could go up in flames because they were fitted with combustible panels that did not meet building regulations. But the body did not check whether it had given approval to any such blocks, the public inquiry into the disaster heard on Thursday. The warning, from a facade manufacturer, came at a construction safety conference in January 2016 addressed by Steve Evans, head of technical operations at the National House Building Council (NHBC). It prompted the event chair to ask if “we are sitting on … a timebomb”. The inquiry has already found that combustible aluminium composite (ACM) panels applied to Grenfell Tower between 2014 and 2016 were the main cause of spread of the fire that killed 72 people. A similar warning of “grave concern” was sent by the same manufacturer to the government’s senior civil servant with responsibility for fire regulations, Brian Martin. He replied that such panels should be tested but “if the designer and building control body choose to do something else then that’s up to them”. The evidence came as the government applied sanctions to a sister company to the Grenfell Tower refurbisher Rydon, suspending it from the help-to-buy scheme which allows first-time buyers to get cheap loans on new homes. Michael Gove, secretary of state for levelling up, housing and communities, said the move against Rydon Homes was due to “the extremely concerning evidence heard by the Grenfell Tower inquiry” about Rydon Maintenance Ltd’s role as the main contractor on the disastrous refurbishment. The move, more than a year after the evidence emerged, comes as the inquiry begins to investigate whether ministers and officials knew about, but failed to tackle, risks posed by dangerous building techniques. Gove said: “I will continue to go after those who put lives at risk, are responsible for the building safety crisis and are failing to play their part in fixing it.” Earlier, the inquiry heard how the “timebomb” issue was raised in the wake of a huge cladding fire in Dubai. In a question-and-answer session at the industry conference Nick Jenkins, a senior technician from Booth Muirie, which manufactures cladding systems, said: “You could have an exact repeat of the Dubai fire in any number of buildings that we supply product to in London.” Jenkins said he felt “real concern” because over the last 15 years his firm had only supplied limited combustibility cladding on two projects in the UK. The rest, he implied, was combustible. This was because of ambiguity in the UK government’s building regulations, policed in part by the private organisation NHBC, over whether panels that were not of limited combustibility were allowed on high-rise apartments. Evans told the inquiry he had trusted that the NHBC hadn’t signed off such buildings for approval, but admitted that even after Jenkins had raised the threat, he was not aware of any effort to check if they had. Under cross-examination by the counsel to the inquiry, Richard Millett QC, he said he “didn’t have a view” at the time on whether Jenkins was right to consider it a grave concern and he was only focused on buildings under construction, not projects that had been completed. He said it might have been a case of “not joining up all the dots”. The inquiry heard Jenkins was so worried he also wrote to the government. Martin said full-scale tests were needed to determine whether such panels were safe. When Jenkins replied that he believed no full-scale tests had been done, and the number of tall buildings with ACM panels that do not meet building regulations were “many and … growing”, Martin conceded that he was doubtful even ACM panels with fire retardant cores would pass tests. Lawyers for the bereaved have already told the inquiry that Martin was “fully aware” of the dangers of combustible materials on high-rise blocks. Martin is currently head of technical policy in the building regulation division at the department of levelling up, housing and communities. He is to give evidence in the new year. The inquiry continues.