Royal Bank of Scotland will invest around £150m a year to improve the resilience of its computer systems, the bank's chief administration officer Simon McNamara said today. 

The bank was hit by another IT failure yesterday which led to 600,000 customer transactions not being processed, resulting in thousands of customers missing out on payments such as wages and benefits. 

The bank, which owns Ulster Bank here, had said last year it would invest an extra £750m in the security and resilience of its IT systems by the end of 2015 to prevent a recurrence of its past problems. 

McNamara said that investment had left it better placed to deal with failures but the incident this week had showed there is more work to do. 

"Technology will on occasion fail. If and when that occurs, we need to ensure we can mask the impact on customers and recover as quickly and effectively as possible. It is important that it is handled well and competently," he said.

McNamara said the bank was very close to resolving the payments that failed. It said yesterday some customers would have to wait until Saturday to receive payments. 

"We have a number of people who are working round the clock,using the skills and tools we have acquired to resolve this issue," he said. 

RBS has been criticised by furious customers on social media since the failure, which affected customers at each of its brands, which also include NatWest and Coutts. 

A spokesperson for Ulster Bank yesterday said the IT issues were limited to a number of Nat West and RBS account holders in Northern Ireland and none in the Republic of Ireland. 
              
The bank was fined £56m last year by Britain's financial regulators for a system breakdown in 2012 that left 6.5 million customers unable to make or receive payments for days. 

Some industry sources say RBS's systems are outdated and made up of a complex patchwork of systems after dozens of acquisitions. 

McNamara said the investment already made had left the ban kbetter placed to deal with the latest failure. 

"It is not feasible to have 100% faultless systems. We will have issues. How we respond to those issues, how we minimise them and how we fix them, is crucial," he said.