The retail giant's financial services business is in the final stages of moving operations over to its own systems and infrastructure based on the Fiserv Signature platform.

Over the weekend it transferred savings and loans products in-house from its old joint venture with the Royal Bank of Scotland, which it bought out in 2008.

The switch left some of the unit's 6.5 million customers unable to access their accounts for a brief period although a spokesman told the BBC the issue has now been fixed.