RBS is set to announce the sale of 318 branches to Spain's Santander as the UK lender offloads the former Williams & Glyn's network.
Santander beat off rivals, including National Australia Bank, in a bid to extend its reach on the high street for an estimated £2bn, according to The Telegraph.
Several thousand staff currently employed by RBS will be affected by the sale, although the final branch network organisation is yet to be announced.
The European Commission forced the sale on RBS before it would approve aid for the bank, which was part of the UK Government's billion pound rescue package.
Following the deal, Santander will have over 1,600 branches in the UK, making it the fourth biggest network in the country after Lloyds Banking Group, Barclays and RBS, and ahead of HSBC.
RBS is set to report its half-year financial results on Friday, which are expected to show a return to profitability under CEO Stephen Hester.
Last month, RBS easily passed the European Union's bank stress test, while a report from the Asset Protection Agency, which runs the UK's Asset Protection Scheme, said the bank was on course to exit the insurance policy within the next two years.
Williams & Glyn's' brand fell out of use nearly 25 years ago, while the branches are mostly in the northwest of England, though seven currently branded as NatWest are in Scotland.
The RBS branch buy up is the latest move in Santander's major and ongoing expansion plans in the UK, which began with the purchase of Abbey and followed up by the acquisition of Alliance & Leicester and parts of Bradford & Bingley.
