The UK’s Financial Conduct Authority (FCA) announced on Tuesday a formal investigation into Royal Bank of Scotland’s (RBS) IT failure which affected customers during the summer of 2011.

The glitch left 17m customers of RBS and subsidiaries NatWest and Ulster Bank unable to access their accounts for up to three weeks.

The FCA stated that it has "started to conduct an enforcement investigation into the IT failures at RBS and will decide whether or not enforcement action should follow that investigation."

The FCA’s unusual decision to announce the investigation stems from the widespread public interest around the issue.

In a statement RBS said the IT failure was "unacceptable."

The newly formed FCA began regulatory work after the Financial Services Authority disbanded in April 2013.

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