Energy supplier E.ON has been ordered to pay a £3 million penalty by industry regulator Ofgem.
The firm was unable to prove that it distributed free energy-saving light bulbs to consumers, with some of them having been sold in Ireland.
Tony Cocker, chief executive of E.ON UK, apologised for the mistake and stated that the necessary changes have been made after talks were conducted by Ofgem.
"Overall energy efficiency obligations have been met, with the shortfall being made up by additional measures. No consumers were misled because of this mistake, but this does not take away from the fact it was an error that should not have been made," he said.
It was revealed that some £2.5 million of the energy supplier's penalty is going to be used to reduce the bills of vulnerable households.
E.ON is one of the big six energy suppliers in the UK, along with rivals in the sector British Gas, EDF Energy, npower, Scottish Power and SSE.
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