Lader revealed the growth of direct and interactive as he delivered an upbeat speech at the firm's AGM, reporting revenue growth in all regions including a 14% rise in the UK during the first five months of 2005.
Lader said revenues at the end of May were up 6% on last year's figures, excluding acquisitions such as the £730m purchase of Grey Global Group and currency fluctuations.
"Media investment management continues to show the strongest growth of all our communications services sectors, along with direct, internet and interactive, and healthcare communications.
"Direct, internet and interactive-related activities now account for almost 15% of the group's revenues," Lader said.
He added that advertising businesses, such as JWT and Ogilvy & Mather Worldwide, performed well as did the group's PR and public affairs companies, including Hill & Knowlton.
The group's fastest-growing region, as in 2004, remains Latin America, with Asia Pacific also performing well.
The UK and US markets continue to grow, however Lader said some markets in Germany, France, Denmark, the Benelux countries and Portugal remained "difficult"
He also told the meeting that the group would continue its policy of encouraging link-ups between its companies.
Despite Lader's optimism, concern still remains among shareholders over the lack of a succession plan over a replacement for chief executive Sir Martin Sorrell should he retire.
The concerns were aired last week by shareholder activist group RREV, run by corporate governance body ISS and the National Association of Pension Funds.
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