
The body, which currently has a media buying roster comprising Carat, Starcom, MediaCom, I-Level and Posterscope, confirmed that it wants to consolidate its business into a single agency to create a "centralised media buying framework".
The COI claims that by integrating its marketing communications across all media, it can produce more effective campaigns and cut costs.
In a statement issued today, Peter Buchanan, the COI's deputy chief executive, said: "Our media buying performance has been outstanding with nine years of continuous improvement and very impressive results compared to the Billett's pool," he said.
"The support we have received from our clients has been a key factor in this success.
"However, the market is changing with the integration of on and offline, multichannel media ownership and deeper partnerships with media owners."
He added: "COI needs to maintain a market-leading position and continue to deliver the very best prices for all our clients."
The COI said it would welcome applications from single agencies, as well as holding companies and consortia.
Agencies interested in applying must register at coi.bravosolution.co.uk and complete a pre-qualification questionnaire by 25 September.
The COI's existing media buying is divided between Carat, which handles the buying for TV and cinema; MediaCom, which handles press; I-Level, which handles digital; Starcom, which handles radio; and Posterscope, which handles outdoor.
This latest move follows an internal review process at the COI managed by Radio Advertising Bureau founder and media industry expert Douglas McArthur OBE, which began in 2007.
The COI works as a centralised purchasing body for the UK government in the context of the Public Contracts Regulations 2006.