The report discloses how much of the energy supplied by UK's major energy suppliers is generated from renewable, nuclear, gas or coal-powered sources.
Commenting on the release of the data, energywatch's head of campaigns Jonathan Stearn said: "This data will give consumers more information about how suppliers source their own electricity.
"The next step is for Ofgem to bring forward an accreditation scheme and new guidelines for green tariffs that will provide confidence and clarity for consumers who want to cut their own carbon footprint."
energywatch was established in November 2000 to protect the rights and interests of gas and electricity customers in the UK.
The organisation is also planning campaigns to name and shame companies that do not offer good service to their customers.
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