Affected Halifax customers will receive an average of £1,666 each
The Halifax is to make "goodwill" payments to 300,000 mortgage customers of a total of up to £500m.
The bank, now part of Lloyds Banking Group, admitted confusing customers about its right to put up the cost of their standard variable rate mortgages.
The Halifax raised the margin on some of these mortgages from 2% to 3% above base rate in January 2009.
The payments have been agreed after a deal with the Financial Services Authority (FSA).
"The group is committed to running its business with the highest levels of integrity and treating its customers fairly, and therefore believes that a proactive co-ordinated programme to identify affected customers and make goodwill payments is the appropriate course of action," Lloyds said.
http://www.bbc.co.uk/news/business-12524732