UK court’s decision on BHP dam collapse a ‘significant landmark in mass action litigation’

The claim, brought on behalf of 620,000 alleged victims, including individuals, businesses and local governments, seeks up to £36 billion in compensation.

The recent decision relates to the liability phase of the inquiry with a trial on damages to follow. BHP has also signalled an intention to appeal.

In 2015, the Mariana dam collapsed, releasing over 40 million cubic metres of iron ore tailings into the environment. The property damage was significant, as were the environmental consequences which stretched hundreds of kilometres across Brazil. It has been described by commentators as Brazil’s worst environmental disaster.

The dam was owned and operated by Samarco, a joint venture in which BHP Brasil Ltd was a 50% partner. BHP UK and BHP Australia were sued for damage arising from the collapse as the parent company of BHP Brasil.

Jacqueline Harris, an environmental litigation expert at Pinsent Masons, said: “An obvious headline from this case is its size. It was initially struck out by the High Court in 2020 because it was considered ‘irredeemably unmanageable’ to proceed in England. The Court of Appeal reversed that decision in 2022, finding that unmanageability was not a basis to refuse permission.”

“The case proceeded as a group litigation, with specific case management directions being made to manage its size but without a group litigation order. The court evidently felt that its case management powers were sufficient to take on the challenge. The speed in which it then heard the case, and issued judgment, appears to have proven it correct – although this is only one stage of the process and allowing for appeal processes the proceedings may be a significant way from conclusion.”

“This is a statement case insofar as the English courts are concerned. It has shown they’re willing to accept and find ways to manage claims of this magnitude and complexity.”

Despite the collapse happening almost 9,000km away, the claimants were allowed to bring an action in the High Court in London because, at the time, BHP UK and BHP Australia operated as a dual listed company, with one of those listings being on the London Stock Exchange.

The court’s role was to determine whether BHP was liable for the dam’s collapse under Brazilian law. It heard from experts on Brazilian law to establish an understanding of the relevant liability regimes. It then applied the facts of the case, as it determined, to that understanding.

Katie Hancock, an environmental litigation expert at Pinsent Masons, said: “Litigating in England in relation to the actions of foreign subsidiaries abroad is not a novel situation.”

“Other recent decisions, such as in the Dyson, Alame and Brazil Iron cases, have shown a willingness of the English courts to hear litigation which relates to events which took place overseas. Indeed, they have done so even when the courts accept that a claim has a closer connection to another jurisdiction than it does to England.”

“England is seen as an attractive jurisdiction for claimants because of the availability of conditional fee agreements and damages-based agreements, and because claimants in group claims such as this are often able to obtain litigation funding to cover their costs of bringing proceedings. This, aligned with a well-structured court system and the usual rule that a successful party recovers much of its costs, makes it attractive compared to other jurisdictions where access to justice is traditionally more challenging for claimants.”

“Those decisions, and now this decision, are likely to only further encourage claimant groups to bring claims in England for alleged actions of English-headquartered companies’ overseas subsidiaries or ventures.”

“That risk is yet to materialise in full, and so is unlikely to dampen the appetite of corporates to headquarter themselves in England for the time being. But should this case act as a lightning rod for claims of this ilk and magnitude in England, then there is a real risk that corporates could begin to re-evaluate the locations of their registered offices. In a worst-case scenario, such a rethink could have a significant impact on the UK’s broader economic growth,” she said.

The High Court found that BHP was liable for the dam’s collapse on two grounds.

One was on the basis of fault-based liability. The court considered that BHP knew or should have known that “internal drainage of the dam was inadequate to prevent saturation”, which led to its collapse. This foreseeability created liability under Brazilian law.

Second was on the basis of strict liability. Brazilian law imposes strict liability on “polluters”, whether direct or indirect.

Calum Atterbury of Pinsent Masons said: “The question of strict liability was ultimately whether BHP had sufficient control over the operation of Samarco to qualify as a ‘polluter’ under Brazilian law.”

The court found that Samarco’s governance structure ensured that BHP’s “interests were always represented” and Samarco was “subservient to the will of BHP”. BHP was also found to have assumed responsibility for “risk assessment, control, mitigation and management within the BHP Group and specifically within Samarco”, alongside exercising “control over Samarco’s activities, including its short and long-term strategy, investments, production, financial and technical risk assessment and management through the audit process, funding arrangements and the payment of dividends”.

Having made these findings on BHP’s control over Samarco, the court held BHP was in sufficient control of Samarco to be considered directly and/or indirectly responsible for the activity of Samarco which caused the collapse.

“This case is one of a number currently progressing through the English courts in which it is alleged that English-headquartered companies owe a duty of care for the activities of overseas subsidiaries or ventures,” said Atterbury. “Such cases have been watched eagerly for any hints on the factual circumstances in which control might be deemed sufficient to establish a parental duty of care.”

Hancock added: “Although the court’s findings were based on Brazilian law, the formulation of the standard of care applied echoes that in English negligence claims. Judicial commentary on the extent to which BHP exercise control over Samarco should, therefore, be informative not only for any future foreign law claims in England, but also for future English law tort claims.

A settlement agreement had been entered into by BHP, BHP’s venture partner Vale and the Brazilian government which provided a $30 billion fund for remediation and compensation in relation to the disaster. From this, and other agreements, BHP argued that around 200,000 claimants had received compensation and waived their claims. The UK proceedings were, therefore, argued to be heavily duplicative.

The court did not confirm whether this was the case, instead finding that the circumstances around each settlement agreement were outside the scope of the present trial. It did, however, state the relevant Brazilian legal principles which would be necessary to determine validity and interpretation of any Brazilian settlement agreements.

“Although the court did not consider the Brazilian settlement agreements a necessary part of the proceedings on liability, they will undoubtedly feature heavily in any future trial on damages,” said Atterbury.

BHP has signalled an intention to appeal the decision, but the lessons of this judgment remain irrespective of whether it is upheld, said Jacqueline Harris.

“The significance of this case is more than the sum of its parts,” she said. “England is rare in its position as home to many significant multinational corporations with large overseas operations. This, coupled with their newly evidenced ability to deal with truly vast claims, has signposted the jurisdiction as a natural home for future mass actions.”

“Following this decision, businesses should consider assessing their management frameworks to understand any potential exposure to lawsuits associated with their overseas businesses and ventures. This case is the first of such magnitude, but unlikely to be the last. If there are steps which can be taken to mitigate the risks, then they should be considered now. The repercussions of failing to do so could have a price tag in the billions.”

Editor's note 26/11/25: This story was updated with additional comments post-publication.