By Maria Ward-Brennan The most significant action of its kind will kick off in the High Court on Monday. Mining giant BHP faces a multi-billion pound lawsuit over its role in the deadly Samarco dam disaster. On 5 November 2015 the Fundão dam in the south-east of Brazil, operated by Samarco, a 50:50 joint venture owned by BHP and peer Vale, failed and unleashed a deluge of thick, red toxic mud that wiped out the village of Bento Rodrigues. The dam was holding back mining waste, known as “tailings.” The collapse of the Fundão dam killed 19 people and is the worst environmental disaster in Brazil…