Santander UK has been ordered to contact over 270,000 borrowers by the Financial Conduct Authority (FCA), after raising mortgage interest rates without being clear.
The newly-formed financial consumer watchdog said that when the UK division of the Spanish bank increased the interest rate back in 2008, the letters sent to customers did not properly explain how the change would impact them.
Some borrowers did not even receive a letter.
As a result, the FCA has told Santander to send out new letters to customers, who can complain if they think they are entitled to compensation.
Santander said the majority of the borrowers would not have been negatively affected from the interest rate change.