By Ed Ballard

LONDON--The U.K.'s energy regulator said the British unit of Electricite de France S.A. is to pay a three million pound ($4.97 million) penalty after an investigation found that it failed to handle consumer complaints efficiently between 2011 and 2012.

The Ofgem probe was prompted by an increase of over 30% in the level of complaints recorded by EDF Energy when it was switching to a new computer system in 2011.

"Between May 2011 and January 2012, EDF Energy did not have appropriate procedures in place to properly receive, record and process all customers' complaints in accordance with complaints handling rules," Ofgem said in a statement.

Ofgem said EDF Energy cooperated with its investigation and will now pay GBP3 million to help fund a government program for improving vulnerable people's energy security and a helpline for people struggling to pay their bills.

Write to Ed Ballard at ed.ballard@wsj.com

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