It was with a hint of mischief that Labour declared this morning that trade minister and Conservative peer Stephen Green, the former executive chairman of HSBC, had "serious questions to answer" over the drug money laundering scandal. It was this formulation, of course, that George Osborne employed in his now-famous attack on Ed Balls over the Libor scandal.

Labour's cause is aided by the fact that the former is by far the greater scandal. In the words of US senators, HSBC was used as a conduit by "drug kingpins and rogue nations" to transfer billions in illicit proceeds to the United States betwen 2004-10. The bank's culture was, they concluded, "pervasively polluted". It was Green, who left HSBC in December 2010 to take up his ministerial post, who was at the bank's helm throughout the period in question, first as chief executive and then as group chairman.

During his time at HSBC, he was widely regarded as the acceptable face of banking. An ordained Church of England priest and the author of Serving God? Serving Mammon?, a reflection on the morality of capitalism, Green wrote in the New Statesman in 2009 that "the value of our business is dependent on the values with which we do our business. Better risk management, enhanced regulation, codification of directors’ responsibilities in company law – all these things are necessary. But they are not, nor can they be, sufficient without a culture of moral values. As individuals, we do not regulate our behaviour simply by what is allowed under the law. We take responsibility for our actions. The organs of capitalism – businesses, banks and other financial institutions – have to do the same." Laudable words, but Green must now explain why HSCB entirely failed to live up to them.

The bank now faces a "substantial" fine of up to $1bn and a criminal investigation by the US Department of Justice. Should evidence emerge that Green was either unwilling or unable to intervene, his position could be under threat.