The group blamed the decline in profits largely on its hi-tech media unit CMP, which accounts for one third of group revenues, as its share price slid to 565p at 10.15am in London.
CMP, which publishes Information Week, Internet Week and Network Computing, saw profits almost halve to £35.4m from £70.7m last time in the face of the downturn in the US advertising market.
Advertising page volumes were down by 26.1% across the market, but United chief executive Lord Hollick said the business had maintained total yields to last year's levels.
However, United's market research operations continued to grow with the acquisition of US market research firm Roper Starch International for $88m (£61.5m).
This acquisition, coupled with the purchase of Allison Fisher International in June for $45m (£31.5m), sees United's market research revenues grow to £200m annually. It also gives its NOP World unit a significant boost in the US, which accounts for 40% of global market research spend.
Earlier this year, United began to dispose of its non-core business-to-business operations. In April, it sold its Megastar website and offloaded its 50% stake in LineOne to Italian ISP Tiscali. In June, it closed Trivanti, its technology joint venture with Psion, and rationalised the Farmgate web business.
It has reduced online investment by £71m to £20m in the current financial year and axed 700 jobs in an attempt to meet its cost-saving targets of £60m.
Earlier this week, it was revealed that its music site Dotmusic was to cut most of its staff and be integrated with the planned business-to-business website of its trade title Music Week.