Survivors of the Grenfell disaster have tried to shame the French government into delivering key witnesses to the public inquiry using a truck-mounted poster outside the country’s embassy in London showing the burnt-out tower at the heart of the tricolour flag. The stunt on Monday came as Grenfell United delivered a letter to the French ambassador to the UK, Catherine Colonna, calling on the French government to publicly urge three former employees of a French cladding company implicated in the fire to give evidence. Three witnesses, including Claude Wehrle, the head of technical sales support at Arconic, which made the plastic-filled aluminium cladding panels that were the main cause of fire spread, have refused to attend. They are citing a rarely invoked 51-year-old statute that prohibits people from disclosing commercial or industrial information to foreign judicial and administrative proceedings. The inquiry has already heard that Wehrle knew in the years before Arconic’s panels were sold for use on Grenfell that they were “dangerous” and showed “bad behaviour exposed to fire”. Seventy-two people died as a result of the fire on 14 June 2017, which spread, through the cladding, from the fourth to the 24th floor in less than 30 minutes. Speaking outside the French embassy in Knightsbridge, Karim Mussilhy, who lost his uncle, Hesham Rahman, in the fire, said: “We need these people to come to the country and tell the truth. It is in the interests of public safety. Thousands of people are living in homes with the material that caused the spread of the fire, caused the death of our families, and they must come here in the interests of public safety and tell the truth. They must stop hiding behind French law. They must come, tell the truth, so we can make sure this never happens again.” The image posted on the truck featured the burnt-out tower, which is not usually used by survivors’ groups because it risks causing upset and trauma. But Mussilhy said: “We felt we had to show the damage these materials did. We need to remind Arconic, the French government and the witnesses what this is about.” The letter to Colonna from Grenfell United’s chair, Natasha Elcock, who escaped with her family from the 11th floor of the council block, said: “We are writing to you today to implore the French government to help us in our quest for truth and justice. “Three key witnesses with information about the cause of the fire are hiding in France, citing the French blocking statute as an excuse for refusing to attend the inquiry … A public statement from the French government urging full cooperation of its citizens … would send a strong message that they cannot hide.” Arconic has denied wrongdoing and said the main fault lay with those responsible for the refurbishment. A spokesman declined to comment on the impasse, but referred to last month’s statement to the inquiry by its counsel. Stephen Hockman QC said three individuals had taken their own separate legal advice and were “to date at least” declining to give oral evidence. “Whilst the company obviously can’t control whether any witnesses testify, the company remains willing to do what it can to assist the inquiry in working with the French government,” he said. Inquiry officials are in talks with French government officials and the UK Foreign Office. The counsel to the inquiry, Richard Millett QC, has said he will “empty-chair” the witnesses if they do not show up, and read out questions they should answer. A French official source said the government’s position was that the inquiry’s requests “do not appear to fall under the scope of … the French blocking statute.” “We have made it clear to Arconic that we do not share their point of view with its refusal to comply with the summons and its wish to avail itself of the blocking statute,” the official said. “We have asked Arconic to shoulder its responsibility in this matter. We have informed the inquiry and the UK Foreign Office of our position. [The purpose of the blocking statute] isn’t to obstruct the emergence of the truth or to guarantee immunity for French nationals. This is not a way to evade responsibility.”