Starcom Mediavest has snatched COI Communications' £20 million radio buying account from the incumbent, OMD.
The surprise win is some compensation for losing the Government's £70 million TV business to Carat in April after 13 years. It also allowed Starcom to turn the tables on Carat, which was shortlisted for the radio account along with OMD, MindShare and ZenithOptimedia.
The battle for the radio business turned into a re-run of the TV pitch, climaxing in a shoot-out between Starcom and Carat.
OMD has held the radio business for four years and was widely tipped to retain it.
In its pitch, Starcom offered COI a "step change", saying the Government's position as the country's biggest radio advertiser at a time when spending was in decline provided a unique opportunity to get better value for money.
It beat its rivals on the media costs it could negotiate, the quality of its work and its fees.
Peter Buchanan, COI's deputy chief executive, said: "The quality of presentations was very high and the competition close. However, it became clear Starcom had a competitive edge." He added: "OMD has done an excellent job. We have no criticism of what it has done for us in the past four years."
Jeremy Found, COI's head of media, said: "COI acknowledges and understands the value of radio as a communications medium. Therefore, we have invested a lot of time assessing each agency and reaching a decision. We look forward to working with Starcom on future campaigns."
The new contract is expected to come into effect from July, following a short hand-over period. The Government's radio spend over the past three full financial years averaged £20 million per year.
COI, which is reviewing its rosters to coincide with the general election, is assessing bids to join its list of 28 creative agencies and is due to announce the results next month. In July, it will hold pitches for its press buying, held by MediaCom, and cinema buying, currently with Universal McCann.
The chairman of Starcom, Jim Marshall, declined to comment.