The massive IT crash at TSB bank last year was caused by moving to a new banking platform before it had been properly tested, an investigation by law firm Slaughter & May has found.
TSB is currently owned by Spanish bank Sabadell.
“TSB went live with a platform that was, in the event, neither stable nor complete,” the report concluded.
The report found TSB’s board failed to fully understand the scope and complexity of the new system before its failure, which led eventually to then CEO Paul Pester leaving the firm.
The report also found that Sabadell’s IT arm Sabis had not been ready to operate the new platform and had failed to test one of two data centers it relied on prior to the launch.
The IT crash locked out nearly two million TSB customers and halved Sabadell’s profits last year.
The system failure led to weeks of TSB customers being unable to access their money and a number of fraud attacks.
TSB now has a new chief executive, Debbie Crosbie, who is due to outline her strategy for TSB next week.
TSB recently took back direct control of important parts of its IT infrastructure away from Sabis, the in-house IT provider of Banco Sabadell.
Sabadell chairman Josep Oliu said in March it is possible that TSB could be merged or sold after it completes a turnaround that could take three years.
Pester criticized Slaughter & May’s “scattergun approach” to its investigation in a statement on Tuesday and attempted to shift blame to Sabis.
“If these findings are right, Sabis rolled the dice by running tests on only one of TSB’s two new data centers and this decision was kept from me and the rest of the TSB board,” he said.
TSB chairman Richard Meddings said: “On behalf of everyone at TSB, I want personally to apologise again for the service disruption which customers experienced during the spring and summer of 2018.
“I would also like to thank everyone at TSB for their significant efforts and commitment to putting things right for our customers and for getting the bank into the position it is in today.
“When we commissioned Slaughter and May to carry out this review, we specifically asked for a fully independent and thorough inquiry.
“Although the report doesn’t paint the full picture of migration, the board were absolutely clear that we wanted to be transparent and learn fully from those aspects which went wrong.
“That is why we have taken the decision to publish this report in full.
“Importantly, TSB has evolved to be a better business than the newly created bank which began the migration project.
“We have already made major changes as a result of what we have learned, including moving to take direct control of our IT operations.
“With the leadership of Debbie Crosbie as our CEO, we are now well on track to get TSB back to what it does best: serving customers and bringing better choices to UK banking.”