The £12m process, incorporating 1300 branches, will be completed by the end of 2010.
Santander uses its brand in more than 40 countries, but, to date, it has received UK exposure only through its sponsorship of the Formula One British Grand Prix.
Recent ads for its UK high-street banks have also carried the line 'We are Santander'.
Chief executive of Santander's UK businesses, Antonio Horta-Osorio, said that bringing the brands together would make it easier for customers to manage their finances.
Forum, page 22.