United, which owns business magazines, research firm NOP and 35% of terrestrial TV station Five, said it had launched a search for a replacement and is looking at internal and external candidates.
Lord Hollick heads the firm that once owned Express Newspapers, before selling it to Richard Desmond in 2001, and also owned the ITV franchises Anglia, Meridian and HTV, which were sold off after its failed merger with Carlton in 2000.
Lord Hollick said: "I plan to leave United in May 2005 when I will be 60. I have had the privilege of working for a great company with an outstanding management team. I look forward to moving on to new opportunities.
"My successor will be chosen from a range of strong internal and external candidates. The board plans to announce my successor by the end of this year."
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