Millions of NatWest customers were unable to make payments through the bank’s website yesterday, as the system crashed for more than four hours.
The failure is the latest in a series for the RBS and NatWest group, which is engaged in an expensive struggle with outdated IT systems.
A key cause of this problem is that its IT systems were formed over years of mergers and acquisitions with other lenders.
The biggest crash came over several weeks in the summer of 2012, and left millions of customers unable to make payments, check their balances or access their accounts properly.
Regulators fined the group a total of £65m for that failure.
Other crashes occurred in the March and December of 2013.
Yesterday’s problem was resolved in the afternoon, with services resuming at around six o’clock.
When the service was down, RBS asked customers to use the telephone banking service, or to visit branches.
“We apologise to customers for the inconvenience,” the group said in a statement.