According to the group, up to 16 million people across the UK could be charged more than they should, with a third of customers receiving estimated bills this quarter.
Robert Hammond, from Consumer Focus, told the BBC it was in "consumers' interest" to carefully check meter readings.
"Consumers could be paying higher prices for gas or electricity used in the past, while for companies it results in a very nice windfall," he added.
The Scotsman reported earlier this week that rising energy prices have resulted in a 40 per cent increase in the sales of wood burning stoves in Scotland in 2008.
Over the time period, energy prices have risen by 38 per cent.
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