Yes, the sale of branches of Natwest in Scotland and RBS in England to Santander was forced upon Nat West/RBS by the European Commission. The idea is that it will increase competition, but as Santander seem to be dominating the High Street I'm not sure of the logic.
Nat West in Scotland is not allowed to encourage its customers to move to its sister company RBS, and vice-versa. Customers can transfer to whichever bank they want but it looks as if they have to keep this pretty quiet. The FAQs on their website
http://natwestbranchinformation.com/home/faq do not include the most obvious question which is "Do I have to move to Santander?".