The regulator said Economy Energy – which recently went bust – agreed the sale of around 30,000 customers to E in December 2018 but failed to notify Ofgem about it when the company stopped trading.
It believes the contract between the two suppliers may no longer be effective as a result of Economy Energy ceasing to trade and the appointment of OVO Energy to take over its customers.
Ofgem said it has issued the provisional order “to prevent further harm and uncertainty” being experienced by former customers of Economy Energy, while it investigates the transaction.
The customers are currently in the process of being fully set up with OVO Energy.
The provisional order will remain in place for three months, during which period E must stop the switch of the customers and write to Ofgem about what steps it has taken.
The issuing of the provisional order, however, does not imply the regulator has found conclusive evidence of a breach at this stage.
Economy Energy’s former customers are being advised to not switch to another supplier until their account has been fully set up with OVO Energy and take a meter reading when ready for when they are contacted over the coming weeks.