Banks should restructure IT systems to provide better services, as many are failing to sell new products to existing customers, according to research firm Forrester.
Forrester said disjoined IT systems and the careless use of data was causing customers to distrust their banks.
Martha Bennett, vice president of research for Forrester, told ZDNet UK sister site silicon.com: "There is data over too many places and that is difficult to use. Say I want to make a payment online and the computer crashes, so you walk past a bank to ask about that payment. You go up to the counter and they say, 'We have nothing to do with the online stuff.'
"The IT implications are having applications in place that allow your staff to be up-to-date regardless of how your customers contact you. It's about the visibility of customer transactions but you need technical platforms to support that."
Bennett said banks need to use more behavioural analysis techniques to personalise the service they offer.
She said: "It's all part of data mining — to marry existing data with behavioural patterns. There is too little thinking about how easy it can be to appear more customer-friendly. So a lot of this is not really about one single technology but how you are more able to appear to be caring."
A study from Forrester found that although customer satisfaction with banks is high in Europe (64 per cent), around a quarter of respondents are likely to buy financial products from a company other than their own.
Speaking at this week's Forrester Financial Services Forum, Cliff Condon, a Forrester principal analyst, said: "People will not necessarily buy their next product from that bank. Trust is eroding — 33 per cent of consumers said their financial institution treated them fairly. They are also sceptical of advice from banks."