The paper examines the impact of regulatory intervention on store card interest rates, for a panel of UK store cards. Panel data estimation methods are used in conjunction with intervention analysis so that the impact of the investigations on store card interest rates can be examined. Results suggest that there is a significant negative impact on store card interest rates. The impact of macroeconomic factors and credit card interest rates on store card interest rates are also taken into account, results indicating that store cards and credit cards should be considered as competing sources of credit.