The inquiry continues more than three years after the tragedy (Image: SWNS)

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Of many haunting moments of the Grenfell Inquiry, this week ­provided one of the most disturbing.

Former product manager Jonathan Roper claimed that insulation manufacturer Celotex deliberately exploited “ignorance” within the construction industry, and had rigged fire safety tests.

The insulation foam, known as RS5000, went on to be used in Grenfell Tower.

Where on June 14, 2017, it fuelled the flames of the fire, and released smoke and toxic gases.

The foam was withdrawn from the market shortly afterwards, but 70 people had already died, and two would die later in hospital.

This kind of evidence, where people offered immunity from prosecution simply tell the truth, or some version of it, is one of the points of the long months of the Inquiry.

Jonathan Roper made the revelations this week
(Image: PA)

“We can’t bring our 72 loved ones back from the dead, but we can try to understand what happened – to
stop it happening ever again,” Karim Mussilhy, a bereaved family member of Grenfell United, says.

So, how shocking to hear that four witnesses, employees and former employees of Arconic, which made Grenfell’s cladding, are refusing to give oral evidence to the Inquiry – hiding behind an obscure 1968 French law.

This is despite having what lead counsel to the Inquiry Richard Millett calls “extremely pertinent evidence to give about the product principally implicated in the rapid and fatal spread of the fire”.

Claude Wehrle, Claude Schmidt and Gwenaëlle Derrendinger all live in France, while Peter Froehlich is based in Germany.

Karim Mussilhy's uncle died in the blaze
(Image: AFP/Getty Images)

All worked at manufacturing giant Alcoa, now known as Arconic, and were involved in selling Reynobond panels with a combustible polyethylene core for use on Grenfell Tower.

The inquiry has already heard that one of the witnesses, technical manager Wehrle, sent emails warning Arconic had received test results for its product which were worse than previously admitted, and had even warned bosses the panels were “flammable”.

Now the four witnesses claim that if they give evidence, they could be prosecuted under archaic French law 68-678 – also known as the ‘French Blocking Statute’.

Lawyers for the Grenfell Inquiry say they have only ever heard of one prosecution under this law in over half a century.

For the bereaved and survivors of Grenfell, the refusal of witnesses to appear adds yet more insult to injury.

“What we hear is ‘we’re not coming’,” Karim Mussilhy, nephew of Hesham Rahman who died in the fire, says.

Hesham Rahman died in the fire
(Image: PA)

“Arconic are key players in this inquiry but they are not coming.”

Karim’s message to Arconic is simply this: “72 people died, and your cladding was one of the main causes.

"Come and tell the truth about how that happened.

“You sold your products in this country and profited from public money and now you must cooperate with the inquiry in the interest of safety.

"We need you to help us make sure this never happens again.”

The urgency he feels is on behalf of all those living right now with cladding.

“What people need to understand is this wasn’t a freak accident, it was inevitable,” he says.

The tower was shrouded following the fire
(Image: Getty Images)

“The corporates, the rotten contractors, the dodgy deals all led to these death traps all across the country and it’s not a matter of ‘if’, it’s a matter of ‘when’ the next Grenfell will happen.”

Arconic says it cannot comment beyond the opening statement it made to the Inquiry, where it said: “The Inquiry has been in contact and we understand remains in contact with the French government via the UK Foreign Office in the hope of providing sufficient legal assurances to enable the company’s current and former employees to give oral evidence to the Inquiry without the risk of criminal prosecution.

"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.”

Grenfell United has now set up a petition calling on the Foreign ­Secretary to act.

“72 people died in the capital of the UK,” the petition on change.org says.

“As Foreign Secretary, Dominic Raab must do everything in his power, using all diplomatic channels, to get Arconic witnesses to come to the Inquiry.

“These materials were not just used on Grenfell, thousands of buildings are wrapped in combustible cladding in the UK and around the world.

It is in the interests of everyone that the truth comes out about the company that made the cladding.”

Flames engulfed the 24-storey tower on June 14, 2017
(Image: PA)

The Foreign, Commonwealth and Development Office says it is “working closely with the Inquiry and the French Government on the issue of attendance of witnesses at the Grenfell Inquiry”.

Two UK-based Arconic employees will give oral evidence.

They are former sales managers Deborah French and Vince Meakins.

Richard Millet QC says the days the other four would have given oral evidence will be filled by reading their witness statements and presenting the questions they would have faced.

Mr Millett told the Inquiry he can “only urge Arconic and its witnesses to do the right thing and come and assist the Inquiry”, warning that otherwise people may “take a dim view of their conduct regardless of the legalities”.

Meanwhile, the relatives and the bereaved of Grenfell wait.

“It feels to us like they are trying to keep their name in the shadows,” Karim says.

“Well let’s say their name. Arconic.”

Click here to sign the petition.