It is thought that 3.5m of those customers are active, adding more than a third to SAV’s existing 9.5m customer base.
Santander acquired the credit card business – which provides credit services through firms such as Debenhams – as part of a wider bundle of GE Money assets it bought in 2009.
The pair are negotiating with the stores who use the service to gain their agreement, but expect them to give the thumbs up as the service will now be provided by a specialist operator, rather than a small part of a larger bank. The deal is due to close early in 2013.
Earlier this month SAV revealed plans to start taking deposits, giving it more funding to expand.