The Grenfell Tower cladding manufacturer has spent £30m on lawyers and advisers defending its role in the disaster in an outlay that dwarfs the amount spent on the panels a public inquiry has determined were the main cause of fire spread.

Arconic has been spending at a rate of up to £50,000 a day on lawyers and other advisers, according to corporate filings in the US seen by the Guardian. As well as the public inquiry, it is embroiled in a criminal investigation in the UK with detectives investigating possible corporate manslaughter and manslaughter cases, a civil suit in the US for wrongful death brought by survivors and a consumer protection inquiry in France, where the subsidiary that supplied the Grenfell panels is based.

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The combustible panels on Grenfell were among the cheapest on the market and were made from thin sheets of aluminium filled with a polyethylene core, which melts at 130C and ignites at 377C.

The extent of Arconic’s legal spending will increase concern that the search for the truth about what caused the 72 deaths is turning into a lawyers’ bonanza. Bereaved and survivors, many of whom have voiced anger that Arconic is still able to trade in the UK, said it showed that the “systems are stacked against us”.

Arconic, a Pittsburgh-based $14bn-a-year (£10.9bn) aluminium manufacturing specialist previously known as Alcoa, declined to comment, but said it was offering full support to the authorities as the UK public inquiry continues.

The inquiry has already cost the taxpayer more than £40m, despite only reaching its halfway stage. The second stage of the inquiry will begin in January and is likely to be at least as expensive as it investigates the decisions made in the refurbishment project. Twenty construction, design and materials companies have been granted core-participant status and each will have its own legal team present for much, if not all, of the 18 months of planned hearings. They will pay their own legal bills.

The tower’s former owner, the Royal Borough of Kensington and Chelsea, has already set aside more than £6m for legal costs. It oversaw the decision to shave less than £300,000 from the budget in 2014 by swapping fire resistant cladding for a cheaper alternative. By February this year the Home Office, which is responsible for fire and rescue policy in England, had already spent £2.1m and the London fire brigade, which was strongly criticised by the inquiry chair, Sir Martin Moore-Bick, for failings which cost lives, has spent about £2.8m on external legal advisers.

Saint Gobain, which made the combustible insulation Celotex, and the main contractor, Rydon, are among those yet to declare their legal bills. Nevertheless, the inquiry is on course to cost in excess of £100m with the second phase starting in late January.

“It comes as no surprise how much corporates will spend to protect their reputations and hide from the truth, instead of ensuring people are safe,” said a spokesperson for the survivors and bereaved group, Grenfell United. “Justice is not a fair fight, the systems are stacked against us, the general public. All we can do is keep faith that we have the truth on our side.”

Deborah Coles, the director of Inquest, a charity that supports the bereaved in investigations into state-related deaths, said: “This goes to the heart of the issue about equality of arms for those most affected. We know that where the responsibility of corporate bodies is an issue they will lawyer themselves up with access to unlimited resources. Justice must be not be undermined by those with deep pockets.”

Arconic said it is continuing to “cooperate with the official UK investigations into the Grenfell Tower tragedy”. A spokesperson for the public inquiry confirmed: “There have been no cases of people or organisations refusing to provide evidence.”

In evidence to the inquiry last year, Arconic claimed it was too early for conclusions about what caused the spread of fire and whether the cladding system breached building regulations. It also argued that its panels were not the primary cause of the disaster and that other materials were as much if not more to blame. Moore-Bick dismissed these submissions, concluding that the cladding panels were the primary cause of spread and that they breached building regulations.

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But there is growing frustration among the bereaved about Arconic’s transparency in the US case. The company is arguing that a suit brought in the US courts by survivors should not be allowed because the disaster took place in the UK. Furthermore, in October, lawyers for the survivors were forced to obtain a ruling from the court in Pennsylvania overturning Arconic’s refusal to disclose documents about the period after the fire. It is continuing to resist releasing documents relating to the manufacture and sale of the cladding used on Grenfell that comes from its French subsidiary.

Shortly after the fire, Arconic’s lawyers collected French documents and transferred them to its US databases. Arconic argues that these are not covered by a court order that requires only documents in the US to be disclosed. It is also invoking a French law that prohibits the transfer of documents from French firms for use in foreign legal proceedings.

A spokesperson for Arconic said: “We continue to cooperate with the official UK investigations into the Grenfell Tower tragedy. In the US litigation, we are providing documents from the US companies, but we must respect French legal requirements and restrictions regarding documents from AAP SAS, as AAP SAS, the company which sold its product as one component of the overall cladding system used on the Grenfell Tower, is a French company.”

• This article was amended on 29 November 2019 because an earlier version referred to Royal Borough of Kensington and Chelsea as the tower’s owner whereas it is the former owner.