Spanish banking giant Santander has become one of the largest banks in Britain after buying 318 branches from Royal Bank of Scotland.

The £1.65 billion deal comprises of 311 RBS and seven NatWest branches as well as 47 banking centres including four corporate and three private centres. This brings the total number of Santander branches in the UK up to 1,643, outstripping the 1,369 branches owned by rival bank HSBC.

António Horta-Osório, chief executive officer of Santander UK, said: “The RBS and NatWest branch acquisition will accelerate our growth and improve competition in a sector vital to the UK economy”.

Taxpayer-backed RBS had to sell the branches to adhere to the regulations put in place by the European Union after the government bailed out the bank with £4.5 billion during the credit crisis.

Critics say the sale reduces competition on the high street and is bad for customer choice.

Stuart Davies, Unite officer for Royal Bank of Scotland, said: “A more varied financial services sector which consumers would benefit from has not been delivered by this forced sale. Santander already own branches of Abbey National, Alliance and Leicester and Bradford and Bingley, there is a danger that British customers will have a dwindling number of providers to choose from”.

The European Commission has also told RBS to sell its insurance businesses including Direct Line, Green Flag, Churchill and Privilege.