Australian mining giant BHP is facing the revival of a $7 billion claim over a dam disaster in Brazil, triggering that country’s worst-ever environmental crisis, following a decision from the UK Court of Appeal.

The Court decided to reopen the lawsuit brought by 200,000 claimants after a lower court struck out the lawsuit as an abuse of process last November.

“Whilst we fully understand the considerations that led the judge to his conclusion that the claim should be struck out, we nevertheless believe that the appeal has a real prospect of success,” three Appeal Court judges said in Tuesday’s ruling.

The collapse of the Fundao dam, owned by the Samarco venture between BHP and Brazilian iron ore mining giant Vale, killed 19 and obliterated villages as over 40 million cubic meters of mining waste swept into the Doce river, reaching the Atlantic Ocean, over 650 km (400 miles) away.

The group claim is one of the largest in English legal history and has been brought by law firm PGMBM on behalf of Brazilian individuals, businesses, churches, organisations, municipalities and indigenous people. Tom Goodhead, a PGMBM managing partner, said it was a “monumental judgement” and that his clients felt this was the first time judges had recognised the importance of the case.

BHP, the world’s largest mining company by market value, has labelled the case pointless and wasteful, alleging it duplicates proceedings in Brazil and the work of the Renova Foundation, an entity created by the company and its Brazilian partners to manage reparations and repairs. “BHP’s position remains that the proceedings do not belong in the UK,” it said in a statement. “Issues brought by the claimants are already covered by the work of the Renova Foundation, by existing decisions of the Brazilian Courts or are the subject of ongoing legal proceedings in Brazil.”