Abbey National is rolling out Siebel eFinance to 12,000 users across 755 branches - the largest single project the bank has ever undertaken.
The One-on-One CRM project aims to increase customer retention and improve revenue by boosting the average number of products sold to each customer from two to 3.5.
Ambrose McGinn, head of e-commerce at Abbey National, said One-on-One was part of the company's aim to become a retailer rather than just a bank.
"Customers are far more interested in retail than finance," he said. "CRM will allow us to increase the value of customers by pushing more products and services."
However, the sheer size of the project creates risks. "We have a plethora of legacy systems, which means that there are a number of associated risks," said McGinn. "We have made a massive investment - it must deliver ROI.
"We employ someone specifically to manage benefits realisation on a month-by-month basis."
The Siebel implementation, which will not be completed until well into 2003, heralds a different approach to IT for Abbey National. "We do not want to be a software company," said McGinn. "We will stop building systems, decommission redundant systems and buy 'out-of-the box' software from now on."