Ofgem, the energy watchdog, has released a press release publicising the fact that tenants, in most circumstances, have the right to switch energy suppliers and the landlord cannot stop the tenant from doing so.
The main thing in this matter comes down to who is actually paying the bills. If the bills are paid directly by the tenant then they have the right to choose their own energy supplier as well as change the meters from credit to prepayment. Ofgem
Publishing the guide, Ofgem said: “The key energy right is that where a tenant is directly responsible for paying the energy bill they have the right to choose their own energy supplier. The landlord or letting agent should not prevent this.”
This is rather important confirmation of the fact that the landlord cannot really stop tenants from switching suppliers. This, as some landlords know, may have important implications since you may get the property back with a different tariff /supplier then you thought you had.
They have published a factsheet which you can access here.