Agency sources said that Lexington, headed by MD Mike Craven, had emerged triumphant from a five-way pitch for the business last week.
However, it is understood the final negotiations are still ongoing between Lexington and the Energy Retail Assocation. Neither side could be reached for comment.
Incumbent agency Four Communications was invited to repitch for the business but withdrew after winning another client. Director Jeremy Fraser said he was not aware of the outcome of the pitch process.
The account went out to pitch last month, following the arrival of new head of comms and media relations Peter Jenkins.