A US judge has allowed a case to proceed against UK traders accused of causing an unprecedented crash in oil futures markets after ruling that text messages between the group were sufficient to point towards a potential conspiracy.

The proposed class-action lawsuit centres around trading on April 20, 2020, when the price of benchmark West Texas Intermediate crude oil plunged below zero for the first time on record. Self-employed traders linked to Vega Capital London, a little-known commodities brokerage based in the Essex town of Benfleet, stand accused of making more than $700mn by flooding futures markets to drive the price lower.

Mish International Monetary, a California rare coin dealer that says it lost money that day, alleges market manipulation and violations of antitrust laws. Its civil suit accuses the defendants of buying special “trading at settlement” (TAS) contracts, whose price would be fixed by that day’s settlement value, then conspiring to dump huge volumes of ordinary WTI contracts ahead of the expiry.