You can organize and shop by pricing at YOUR individual usage level, which allows you to shop and compare energy plans based on the rates you’ll actually see appear on your bill, inclusive of taxes and hidden fees. You won’t be misled by the “teaser rates” tied with higher usage levels that many homes never experience, as their usage level never reaches that pricing tier.
You should also check your tenancy agreement – but even if your contract bans switching, Ofgem's guidance on this states that if you pay the energy bill, you're still entitled to change supplier any time. You can still compare on Cheap Energy Club if you don't have the former occupants' bills, just hit the "don't know" button when you enter your usage.
Twenty-nine states have deregulated electricity, natural gas or both. That allows you to shop for the supply portion of your bill from alternative providers who may offer rates lower than the default supplier – usually a utility. Delivery services and billing will remain the responsibility of the local utility as they own the power lines and wires that keep the lights on.