I'm a tenant – am I allowed to switch energy supplier when I move in?

If your name is going to be on the energy bill, you have the right to choose your own energy supplier. 

But your landlord has the right to choose your supplier if they pay the energy bills directly –for instance, the landlord pays the bill and reclaims the money from you; or your energy costs are included in the rent.

How do I get a better energy deal for my new home?