Yes, you should be able to switch energy supplier if you rent your property, but the way you go about it will depend upon who looks after the energy bills.
If you pay the energy bills directly to the property’s supplier, then you’re free to compare prices and switch at any time. If you’ve just moved into a rental property, you’ll be on your supplier’s more expensive standard variable tariff, so you should compare prices to find a cheaper energy deal as soon as possible.
If your landlord pays for the energy to the property, you need to speak to them about switching to the best possible energy tariff to ensure your bills are kept to a minimum. If you have just moved into a property and are not sure who supplies your gas and electricity then you should contact CAfS and start an energy comparison without delay. CAfS may be able to help you with energy advice and tariff comparisons. To see if you are eligible for this free service see https://cafs.org.uk/cafs-draughtproofing-energy-saving-services/