When Jamie Dimon took the helm at Chicago’s Bank One in 2000 he found that the legacy of the bank’s acquisition binge included no fewer than seven different deposit computer systems that needed integrating. His legendary cost-cutting ability helped prepare Bank One for takeover by JPMorgan Chase, and provided the platform for Mr Dimon to become chief executive of the enlarged bank.

Around the same time, Sir Fred Goodwin of Royal Bank of Scotland mounted a takeover of National Westminster Bank in the UK. By integrating technology platforms, he was able to slash NatWest’s cost-income ratio from 65 per cent, compared with RBS’s standalone ratio of 49.5 per cent. By 2003, when the two banks were fully integrated, the combined group’s ratio had fallen to 42 per cent.