The COI spent £112m on advertising in 2010, down from £221m in 2009, when it was the UK's biggest advertiser.
Since coming to power in May, the coalition Government has imposed a spending freeze to ensure that only "essential" advertising is run.
As a result, the COI is now the fifth-biggest spender, according to estimates* from Nielsen.
In comparison, Procter & Gamble increased adspend by 33% from £142m in 2009, to £189m in 2010.
BSkyB was the second, spending £161m, up from £134m in 2009.
Unilever was third with a spend of £132m, having increased its spend by just 2%, substantially less than its FMCG rival, P&G.
Tesco, the biggest supermarket in the UK, was fourth, spending £120m, an increase of 19%.
BT made the biggest increase to its outlay of any top 10 advertiser, lifting its spend by 44% to £104m.
|Advertiser||UK expenditure||UK expenditure||Year-on-year|
|2010 (£m)||2009 (£m)||% change|
|Procter & Gamble||189||142||33|
*The figures cover the year to 15 December and do not include: internet advertising for the period 1 October to 15 December; outdoor, cinema, direct mail and door drop advertising for the period 1 November to 15 December; regional press and magazine advertising for the period 1 to 15 December; or TV and radio advertising for the period 6 to 15 December.