Just before Christmas, the UK banking regulators fined TSB Bank £49m for operational risk management and governance failures relating to a core system migration project that resulted in large-scale disruption to its customers. While this occurred back in 2018 and “hindsight is always easier than the dreadful moment of decision” (Richelle E Goodrich), the scale of the event was such that it worth recalling again as a useful case study of core migration risks. The disruption took over eight months to fully resolve, with a significant proportion of its 5.2million customers impacted, total direct costs from the failure (including the new fine) have reached around £400m now, and its CEO had to resign shortly after the event. Indeed, it proved to be one of the major catalysts for the Prudential Regulation Authority to update its operational resilience policies in March 2021.