Yes, you can still switch, though some smaller suppliers may not take you on.
Previously you had to pay £30-£70 more on top of any comparison quote, as the gas provider must pay both National Grid and the IGT to supply gas to your house. This charge was passed directly on to you. But, now the big six energy providers (as well as most smaller providers) don't charge extra.
Independent gas transporters (IGTs) are often used by constructors instead of National Grid in new-build properties as IGTs charge less to fit pipes. One in twenty people are supplied by IGTs instead of National Grid.