NatWest customers face further upheaval today (Saturday) after technical hitches have left clients unable to pay bills or access their money.

The bank is opening hundreds of branches over the weekend and said it was working 'round the clock' to clear a backlog of chaos.

Although it remains unclear exactly when the issues will be completely resolved more than 900 branches will be staffed until 6pm today and until noon tomorrow.

A statement on the NatWest website said: 'We would like to apologise to all of our customers who have been affected by our current technical issues.

'To help our customers, we will have over 900 of our branches extend opening hours on Saturday June 23 to 6pm.

'These branches will also be open on Sunday June 24 from 9am to 12 noon.

'Staff in our branches will be ready and available to answer any customer questions and help with emergency needs.

'We appreciate that this has caused an unacceptable level of inconvenience, and we are working around the clock to fix this.'

NatWest has more than 7.5m personal banking customers but the group said it could not tell how many have been affected as it was not possible to know when they were expecting payments into their accounts.

The technical fault has disrupted payments to and from NatWest since Thursday and the issues also extend to the Royal Bank of Scotland (RBS) and Ulster Bank users.

All three banks are part of RBS Group and the problem reportedly arose after staff tried to install a software update on RBS's payment processing system, but ended up corrupting it.

Account balances were not updated properly overnight, meaning credit and debit payments were not showing up as quickly as they should.

The group has pledged no one will be left out of pocket and anyone who incurs penalties because of the problems has been urged to contact their branch.

The Financial Ombudsman Service has said that anyone affected should keep a record of how they were financially disadvantaged.