Tesco Bank experienced some problems when it migrated some of its accounts from systems at its former partner Royal bank of Scotland. As reported by the BBC, the bank was moving savings and loans products in-house from RBS.
Tesco set up its own core banking system in November 2009, when it selected an off-the-shelf core banking system from Fiserv, as it moves towards being a full-service retail bank. It went live with the system about 11 months later.
A Tesco spokesman told the BBC: "For a brief period, some customers were unfortunately unable to access their accounts. We apologise for this, but can reassure them that the process is now complete and all customers can access their accounts online as normal."
Changes to systems underpinning Tesco Bank were among the factors prompting an increase in Tesco's capital expenditure last year. Capital expenditure in the UK was £1.7bn, with an additional £200m in the group's banking arm, mainly for putting systems on new platforms.