It has since been said that city regulator the to tell UK banks to upgrade their outdated IT systems, but is waiting to hear the full details of what went wrong.

that the banking group may have avoided the major IT glitch if it had focused more on keeping its existing systems up-to-date, rather than developing new systems.

"RBS has seen a big mushrooming in spending on technology. With hindsight maybe a bit more of that increase in spend should have been in the core, taken-for-granted systems that work every day," said Hester.

"Some of our focus was on the new things people want."