India's state auditor has accused its ruling party of losing the country an incredible $33bn, through selling coal-mining rights to the private sector too cheaply. As you'd expect, Prime Minister Manmohan Singh – who was the minister responsible for coal at the relevant time – has angrily rejected the auditor's report. But the allegations point to fraud on a staggering level.

This isn't the first time. Singh's Congress party has come under continued criticism from the auditor-general for suspect sell-offs of state assets. A scandal over mobile phone licences from 2010 led to the arrest of the minister in charge. But this is the biggest allegation of fraud yet – on a world-beating scale – and it has caused parliament to grind to a halt.

Since 1993, India has been selling off its state-owned coal industry, with a government committee allocating chunks of the lucrative business to private power generators. As minister responsible, Singh rejected a more transparent, competitive process, saying it would be too time-consuming during a period when India's demand for electricity was soaring.

Congress party members have cheered on Singh's robust denial of the allegations. But citizens will not be bought off so easily: water cannon were used on the streets of Delhi against protesters calling for the PM's resignation.

Learn more: Manmohan Singh's government has been hit by a series of corruption scandals, many of them involving the corporate sector. The BBC has a shocking list.

Sources: Financial Times, CBS News, BBC