The bank has warned that it faces potential legal challenges going forward.

It said: "The incident, the group's handling of the incident and the systems and controls surrounding the processes affected, are the subject of regulatory enquiries (both from the UK and Ireland) and the group can become a party to litigation."

"In particular, the group could face legal claims from those whose accounts were affected and could itself have claims against third parties."

In July, millions of RBS customers couldn't gain access to funds in their bank accounts after a botched upgrade that was made to batch processing software CA 7 from CA Technologies, which impacted some accounts for more than a month.

It was revealed that it was RBS' Edinburgh-based IT staff that were responsible for the systems failure, which contradicted earlier media reports that claimed a junior IT worker based in India had made the error.