A large number of NatWest bank account holders, along with RBS and Ulster Bank account holders have been unable to access online services. Technical issues also meant that some balances were not updated with overnight payments.
RBS apologised for the “unacceptable inconvenience” and said customers would not be left out of pocket. The group is keeping over 1,000 branches open until 19:00BST on Thursday to assist customers.
In an update on its website, Natwest said all account information had been updated by late afternoon, but some online services were still unavailable. It said it was working hard to fully resolve the situation as soon as possible.
The banking group confirmed that a number of business accounts had also been affected. One small business owner told the BBC that the electronic system to pay staff was not working.
He said that while the bank’s business service centre had put a note on his account to allow him access to emergency cash, there were no communications within the bank as staff in his branch had no record of it and the note was having to be faxed over.
Many customers have taken to Twitter reporting that they have not been paid and expressing fears that the problem would not be fixed before the weekend.
NatWest has 7.5 million personal banking customers. The bank did not say how many people had been affected across the group, but Ulster Bank, which along with NatWest is also part of the RBS group, said 100,000 of its customers had been affected by “a major technical issue”.
“We are working hard to minimise the impact and will ensure that those who are affected do not suffer any financial loss,” Ulster Bank said in a statement.
Bob Spearman from Petworth told the BBC his weekly tax credit payment had not been paid into his NatWest account.
“We, like many other low-income families live from week to week and the Child Tax Credit weekly payment is a lifeline on which we rely,” he said.
Customers have also reported problems accessing their online accounts for the past 24 hours.
A message posted from the NatWest Help Twitter account said: “This is an unacceptable inconvenience for our customers for which we apologise.”
A spokeswoman for UK Payments Council, which oversees payments strategy, said that the problem did not appear to have affected any other banks.
However, people expecting payments from individuals or businesses which banked with NatWest could encounter problems.
Last week, Royal Bank of Scotland and NatWest launched a mobile banking app to enable people to withdraw money from cash machines using their smartphone.
This marked the latest development in a long-predicted move towards the smartphone becoming a digital wallet.