Royal Bank of Scotland, which owns NatWest, is to spend £1 billion on a three-year plan to enhance its online and mobile services.
The "digital first" investment in personal and small business banking comes in the wake of a 200 per cent jump in customer usage of RBS online and mobile technology in the last three years.
RBS is working on plans to improve the resilience of its systems after a number of online outages, most notably a crash in the summer of 2012 which cost the group £175 million in compensation.
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RBS and NatWest have around six million active online customers.
Under the plans, customers will be able to view and amend regular payments on their mobiles without having to use online banking.
More than 400 branches will be fitted with new technology to allow customers to register and access online banking. It is also adding up to 100 new ATM locations.
Les Matheson, chief executive of personal and business banking, said: "Our customers' needs are rapidly changing. We must respond and continue to improve on the service we offer both online and on mobile."
Chief executive Ross McEwan told shareholders at the AGM this week that branch closures are inevitable.
He said: "The truth is that some branches hardly see a customer, which is why we are taking tough decisions about closing some."