Energy suppliers will not be able to back bill micro businesses for more than a year from November.
Ofgem has introduced a licence condition that covers both gas and electricity.
While some suppliers had already signed up to a voluntary arrangement, the licence condition formalises the requirement.
Ofgem said it was needed because back billing complaints had risen steadily year on year and that many suppliers had not signed up to the voluntary agreement. Even where they had, there are different levels of protection, with some firms only limiting backbilling to several years, rather than one.
See details here.