The energy regulator Ofgem told BBC's Money Box that it is writing to chief executives demanding to know how many people have been sent "back bills". Back billing is when customers receive new bills for energy used longer than 12 months before - a practice that was banned seven years ago.

The energy regulator is gearing up to introduce a series of major changes that could see you shelling out more or less on your bills, depending on your energy consumption

A report by consumer watchdog Citizens Advice claimed that network operators made use of a regulatory loophole set by Ofgem

Ofgem announced plans for more low or no standing charge energy tariffs last year, and has today opened a consultation on how this would work

Standing charges are applied daily, regardless of how much energy the customer uses, and many campaigners say they affect vulnerable customers more.

Every energy supplier could be required to offer tariffs with low or no standing charges, under new proposals from the energy regulator

The energy regulator said it is consulting on bringing in the option under the price cap that would cover so-called zero standing charge tariffs

Standing charges are set by energy suppliers and rack up daily, regardless of how much energy you use that day.