The conservation organisation's report UK Power Giants: Talking Climate Change also evaluates how major suppliers, including British Gas owner Centrica and EDF Energy, are embracing renewable energy technology.
Discussing the findings, WWF's head of climate change Keith Allott said: "The power sector, which accounts for more than 30 per cent of our carbon emissions, will need to decarbonise completely by 2050 if the UK is to play its part in avoiding dangerous climate change.
"Investors should be looking at these reports to see which companies are waking up to that reality and which are lagging behind."
The new report on the UK's major energy suppliers comes after research by consumer watchdog energywatch found that many small businesses were unhappy with the service they were receiving from gas and electricity providers.
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