The licence condition is intended to ensure that households who receive an early smart meter are not disadvantaged or unable to switch supplier without incurring costs. The condition applies to all suppliers.
Additionally, as of next year, large suppliers (those with over 250,000 customers that
have installed, or plan to install, more than 25,000 advanced meters or
5,000 or more advanced prepayment meters) that have provided an advanced meter will have to provide services that enable some smart functionality to a new supplier should their customer decide to switch. Customers must also be told that they may lose meter functionality before they sign up to supply contracts. Suppliers must also delete and cease to flow any ‘misleading’ information relating to to their tariffs once a customer has switched, said Ofgem. Finally, when switching supplier, customers must not be charged if a meter exchange is required to maintain prepayment functionality.
See the document here.