Royal Bank of Scotland
Major British banks have problems with their computer systems through a lack of investment (Reuters)

Royal Bank of Scotland customers may not be the only ones to suffer from their bank's IT shortcomings after a computer systems expert warned that other big British institutions have also failed to invest enough in this area.

Colin Privett, UK managing director for software analysis company CAST, said that major banks could be doing far more to improve their IT systems.

His warning follows an evening of outages at RBS and NatWest which left many customers unable to make payments on Cyber Monday, the biggest online shopping day of the year. Others reported account problems such as incorrect balances showing and not having received welfare payments including child benefit.

"[Software] is a general problem for big banks. They have not invested enough over the years," Privett told IBTimes UK, echoing the message from RBS chief executive Ross McEwan on his bank's computer problems.

McEwan said: "For decades RBS failed to invest properly in its systems.

"We need to put our customers' needs at the centre of all we do. It will take time but we are investing heavily in building IT systems our customers can rely on."

The computer fiasco at RBS was to be expected, according to Privett.

"It is not a surprise to me that these sorts of problems are occurring in financial services as they run very complex systems and have very large volumes going through those systems," he said.

"It was no surprise that it was the biggest trading day of the year when this problem manifested itself. Testing itself will not pick up these vulnerabilities. They [RBS] should be taking a hard look at the code."

Privett said that computer systems at financial institutions were increasingly complex and it was hard to make sure the code they were using worked.

However, he did not "think that all the banks are taking all the care that they could to set up" ways they could check the quality of the code they were using.