What are IGT energy tariffs?

An IGT tariff is for households whose gas supply is delivered by an independent gas transporter, rather than National Grid gas. 

Around 760,000 gas consumers (equal to 3% of all gas consumers) are currently connected to one of the networks operated by an independent gas transporter. The number of IGT network connections is increasing rapidly. 

Three out of the big six suppliers - EDF Energy, Npower and Eon - are currently levying supplemental charges for their customers on the IGT supply networks. The charges for domestic consumers range from £30 to over £50 a year (excluding VAT) for an average user.

IGT supplements are not available on the Which? Switch website at present.