In 2007, JP Morgan did an extraordinary thing: it rejected a chance to advise on, and potentially finance, a $50bn (€32bn) leveraged buyout of Dow Chemical, one of the US' largest companies. The fees from such a deal would have been staggering.

How JP Morgan came to the decision is a tale of two investment banks, both carrying the JP Morgan name. The conflict-review tug-of-war wended its way for months between eager bankers at London-based JP Morgan Cazenove, in a team led by banker Ian Hannam, and more sceptical members of JP Morgan’s US investment bank, led by Douglas Braunstein, who in emails declared himself “intensely uncomfortable” with the talks. (Dow Chemical, in its legal filings, makes the distinction between the two: perhaps because it was the US. investment bankers who blew the whistle to the company on the illicit buyout, Dow’s legal filings refer to “JP Morgan Cazenove” as the bank behind the failed buyout coup.)