The review follows the arrival of marketing director Amanda Mackenzie last year. Mackenzie said: "We enjoy an excellent relationship with all our agencies, who have supported us passionately and tirelessly over the years.
"As a matter of due diligence it is time we paused for breath to see if we can work smarter. If at the end of the review we find ourselves in the same place, that will mean we have the right relationships and the right model to support our business needs."
The review will also mean the utilities giant centralise its print artwork production. The direct marketing pitch process will get under way in December and is due to be resolved by May next year.
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