United said that the global advertising market continued to deteriorate and would have a negative impact on its high-tech publishing arm. It said the worsening conditions would hit its US business-to-business publisher CMP.
The comments came in stark contrast to those made earlier this week by AOL Time Warner CEO Gerald Levin, who said that advertising revenues were stabilising.
In a statement, the company said, "Conditions in the high-tech advertising segment remain very challenging. The results for this division are likely to be below our previous expectations for the year and around the bottom end of market forecasts."
At 10.14 this morning, United's shares were down 21p to 614p in London.
Around a third of United's profits are derived from advertising revenues, but this is set to decline as it continues to expand its other businesses, such as market research, through acquisitions.
United owns market research firm NOP, which has seen strong performances from its healthcare and media measurement businesses.
United's news distribution service PR Newswire is also said to be performing strongly and, although it suffered from lower numbers of IPO releases, this was offset by an increase in earnings and other regulatory releases.
At its AGM in May, United reported a 4.6% drop in advertising page volumes for the 12 months to March 2001, because of the recession in the US advertising market.