Energy suppliers cannot charge you for gas or electricity used more than 12 months ago if they failed to bill you correctly or did not inform you via an account statement. This rule also applies if a supplier raises your Direct Debit because they previously set it too low. They cannot use this to reclaim underpayments older than a year. These protections apply to households and most small business customers unless the customer has prevented accurate billing, such as by refusing meter access or tampering with equipment.