E.on has agreed to pay £2.5 million to help some of its most vulnerable customers and been fined £500,000 after it inaccurately reported how many free light bulbs it gave out as part an energy efficiency scheme.

Under the Government's Carbon Emissions Reductions Target (Cert), large energy suppliers had to deliver energy efficiency measures to consumers in Britain – including distributing free energy-saving bulbs to households (see our Cheap Energy Club for help getting the cheapest energy tariff).

E.on said it distributed 3.4 million bulbs in 2010. But regulator Ofgem found that figure included bulbs which turned up in shops in Ireland, as well as others for which E.on couldn't provide evidence they had actually been given away.

As a result of the error, E.on has agreed to make payments of £2.5 million to directly benefit some of its most vulnerable customers, as well as a £500,000 fine to Ofgem.

The regulator says the £2.5 million payment will mean around 18,500 extra customers will receive £135 to help with their 2013/14 winter bills.

E.on's payment will be made to customers who are eligible to receive its Warm Home Discount Broader Group payments. Customers can check whether they're eligible and apply for the scheme on the E.on website.

'Additional help'

The mistake accounted for 1% of E.on's obligations under the Cert scheme, which ended last year. E.on made up for the shortfall by installing extra energy-efficiency measures.

Sarah Harrison, Ofgem's senior partner in charge of enforcement, says: "This case leaves companies in no doubt that Ofgem takes reporting failures seriously. Accurate company reporting is essential to Ofgem's effective administration of the Government's environmental schemes.

"This settlement means that £2.5 million of additional help will go to some of E.on's most vulnerable customers. Without E.on's constructive engagement, the level of fine would have been much higher."

E.on UK chief executive Tony Cocker, chief executive of Eon UK says: "We're sorry these mistakes were made in 2010 and Ofgem has received a board-level assurance that the necessary changes have been made.

"Our controls should have been stronger and our processes more robust."