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.
On the other hand, month-to-month variable rate (no-contract) plans don’t have cancellation fees. You won’t be penalized if you find a better deal elsewhere and want to make another switch. And, you won’t be stuck paying more than you should be if the market rate for electricity trends down. But, if it goes up, you’ll be paying more than your in-contract neighbors, and you’ll likely want to shop around again for a better deal.