TSB, a UK bank with about 5.2 million customers, ran on Lloyds Banking Group's IT after being split from Lloyds in 2014. After Spain's Banco de Sabadell bid for it in 2015, the plan was to move TSB onto Proteo4UK, a new version of Sabadell's platform, built and run by Sabadell's IT subsidiaries (SABIS).
The big move ran over the weekend of 20 to 22 April 2018, going live on the 22nd. The data itself migrated successfully. But almost immediately online, mobile and telephone banking failed, branch technology broke, and payment and debit card problems followed. All 550 branches were affected.
The direct causes were mostly configuration, capacity and coding. One stood out. The new platform ran two data centres "Active-Active": both live at once, so either could fail without an outage. But a customer's login could be served by one data centre while their next request went to the other, where they had no session. Customers saw "your session has expired". In the first week, digital banking was at times completely unavailable.
A test might have caught some of it. TSB had planned to test the platform at volume in both data centres in Active-Active mode. In the weeks before go-live, it accepted SABIS's counter-proposal to test only one. That decision was taken informally, not documented and not escalated. Testing ran so late that the final report arrived on 17 April, the day before the Board met to approve the last steps.
TSB returned to business as usual in December 2018 and paid £32.7 million in redress to customers. In December 2022 the FCA and PRA fined it £48.65 million in total.
- About 5.2 million customers; all 550 branches affected
- 2 data centres in production, 1 tested
- £32.7 million paid to customers in redress
- £48.65 million in fines: £29.75 million (FCA) and £18.9 million (PRA), after a 30 % settlement discount
Why it matters: Test the system the way it will run in production. One data centre can't show you the bugs that only appear between two, and a shortcut like that should be written down and escalated.