Shares in BP were the biggest fallers in the FTSE 100 on Wednesday morning, dropping 3% to 423p, as the US justice department ramped up its rhetoric against the oil company for the 2010 oil spill in the Gulf of Mexico.

In new court papers, the justice department gave examples of what it calls ‘gross negligence and wilful misconduct’ over the spill, the largest in US history.

The court filing is the sharpest position yet taken by the US government as it seeks to hold the British group largely responsible. Gross negligence is a central issue to the case, set to go to trial in New Orleans in January 2013. A gross negligence finding could nearly quadruple the civil damages owed by BP under the Clean Water Act to $21bn (£13.2bn).

The US government and BP are engaged in talks to settle civil and potential criminal liability, though neither side will comment on the status of negotiations.

‘The behaviour, words, and actions of these BP executives would not be tolerated in a middling size company manufacturing dry goods for sale in a suburban mall,’ government lawyers wrote in the filing on 31 August in federal court in New Orleans.

The filing comes more than two […]