By Marcus Leach

Following a spate of price increases from utility companies Ofgem, the industry regulator, has asked energy firms to explain how they calculate bills that straddle a price increase.

The concern for Ofgem is that customers may end up being overcharged when their bill falls in a period both before and after the introduction of new tariffs.

In recent weeks five of the so-called 'big six' suppliers have increased their prices, with only EDF Energy yet to do so.

"We have written to suppliers yesterday asking each of them to provide details of the approach they take to apportioning price increases and an explanation of the checks they employ to ensure accuracy," an Ofgem spokesman told The Times newspaper.

"We also want to understand the way in which estimated and actual bills are reconciled.

"We want suppliers to explain what mechanisms they use when prices are raised to ensure that consumers pay the higher price only for units consumed following the price increase."

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